PDF Summary:Why Brains Need Friends, by Ben Rein

We’re lonelier than ever, and it’s making us sick—but it doesn’t have to be this way. In Why Brains Need Friends (2025), neuroscientist Ben Rein explains that your brain is wired to thrive when you’re socially connected. For our ancestors, group membership meant survival—so when deprived of connection, your brain triggers a stress response that leads to mental and physical health problems. Yet modern life isolates us by replacing human contact with screens, while our own brains work against us by underestimating how much we’ll enjoy socializing.

In this guide, we’ll explore the neuroscience of why your brain demands connection, how contemporary society creates a dangerous mismatch with our evolutionary needs, and practical strategies for rebuilding your social life. We’ll also connect Rein’s research to the longest-running study of human happiness, complicate his optimistic view of empathy with that of a psychologist who argues it does more harm than good, and examine what decades of research on pets, psychedelics, and body language reveal about the biology of human connection.

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Why Cues Matter for Connection

Communications expert Vanessa Van Edwards sheds some light on the importance of social cues in her book, Cues. She writes that we use cues to both project likability and perceive others’ traits. For example, you might smile to indicate friendliness, or interpret someone else’s smile to mean that they feel friendly toward you. Such cues become especially important in tricky social situations, like when you’re meeting someone new or having a difficult, emotional conversation with a loved one. Our brains have evolved to pick up on these cues in only a few milliseconds, so that we can make quick judgments about whether and how to connect with others.

As Rein notes, the further you move down the ladder of connection, the fewer cues you’re able to project and perceive—which makes it more difficult to connect via technology than in person. Van Edwards says that online, we can use emojis and punctuation strategically to project virtual cues, but they’re not as powerful as their in-person equivalents.

Rein also proposes that social cues play an important role in empathy. When you can’t see someone’s face or hear their voice, it’s harder to connect with them on an emotional level. This helps explain why the internet can be such a hostile place: Everyone feels less empathy when communicating online. Without social cues, your brain doesn’t register that you’ve caused someone pain, so you feel no need to exercise restraint. As a result, we’re all more likely to act like jerks online than we are in person.

The Cost of Making Communication Effortless

In Superbloom, Nicholas Carr points out that every major communication technology for the past 150 years has promised to unite us: People expected the telegraph to end war, radio to foster understanding, TV to create a shared culture, and social media to create community. Carr argues they all delivered something closer to the opposite—not because they stripped away social cues, but because they stripped away friction. The effort to write a letter, travel to see someone, or wait for a conversation created deliberation, investment, and a signal to the other person that they were worth the effort. Apps didn’t just make communication faster, but hollowed out what made it meaningful.

Carr also explains that in online interactions, your brain isn’t just missing the cues that activate empathy, but processing a curated performance rather than a full human being. Carr draws on Jean Baudrillard’s concept of “hyperreality” to name what’s happening: Digital tools that began as stand-ins for real relationships have gradually become the primary thing itself. We follow strangers’ curated performances and call it friendship; we fall in love with chatbots and call it connection. Carr agrees with Rein that if you want real interactions, you have to show up in person—and warns that without in-person conversation, you may gradually lose the capacity for the kind of attention that makes genuine connection possible at all.

How Our Brains Work Against Us

Even if we eliminated every external barrier to connection, Rein contends we’d still struggle because our brains routinely misjudge social situations in ways that discourage interaction. Studies show that we consistently underestimate how much we’ll enjoy conversations, particularly with strangers. We also overestimate the likelihood of rejection: People expect over half of strangers to refuse conversation when the actual rate is zero percent. Finally, we underrate our own conversational abilities—many people rate themselves below average on social skills while rating themselves above average on nearly everything else.

Rein argues that these mispredictions add up to a pattern where we underestimate the benefits and overestimate the costs of social interaction. We do this for evolutionary reasons: In ancient tribal societies, maintaining your standing in the group was a life-or-death matter. If you took a social risk and it didn’t pay off, you might be expelled from your group, which usually meant you wouldn’t survive long. As a result, your brain developed hypersensitivity to social risks—better to be overly cautious than to carelessly alienate your community. Even though rejection in modern life rarely threatens survival, your brain continues to misjudge the risks and rewards of social interaction and influences your behavior accordingly.

How Isolation Trains Your Brain to Expect Rejection

Rein explains that your brain miscalculates social risks, and in The First Rule of Mastery, Michael Gervais and Kevin Lake explain how this happens in the moment. They identify three cognitive biases that work together to inflate your sense of social danger: First, the spotlight effect makes you assume others are paying far more attention to you than they actually are. Second, the false consensus bias means that if you view yourself negatively, you assume others do too. Third, because of confirmation bias, if you expect rejection, your brain actively filters out evidence that you’re wrong. These are the neural machinery that produces the inaccurate predictions Rein describes, like expecting more than half of strangers to refuse a conversation.

Gervais and Lake also show that your tendency to misjudge social situations doesn’t stay fixed, but actually compounds over time. Research bears this out: Lonelier people tend to have lower self-esteem and higher expectations of rejection, meaning isolation doesn’t just reflect social avoidance, but worsens it. The more you avoid social interaction, the more miscalibrated your brain’s threat-detection becomes, making the next interaction feel even more daunting than the last. Rein urges you to override your brain’s faulty predictions and push yourself to engage with others. As you do so, it may help to keep in mind that you’re not fighting a personality quirk, but a self-reinforcing cycle that isolation created.

Why We Struggle to Empathize

Beyond mispredicting outcomes, our brains apply empathy selectively in ways that divide rather than unite us. Rein explains that we’re more likely to extend empathy to people who are similar to us or who belong to the same social groups we do. Research consistently demonstrates this bias: Brain regions that process pain activate more strongly when you view someone of your own race experiencing pain, someone who shares your religion, or even someone who was assigned to the same arbitrary team as you during a laboratory task. This selectivity extends across countless identity markers.

(Shortform note: Rein assumes you can and should try to feel empathy for people unlike you, but in Against Empathy, Paul Bloom challenges that assumption. Bloom agrees with Rein that empathy is selective by nature, but Bloom argues that this isn’t a bug we can fix through effort: Empathy will always illuminate those who feel familiar and leave everyone else in relative darkness. Bloom’s alternative is to cultivate what he calls reasoned compassion: a deliberate concern for others’ welfare that doesn’t depend on whether they feel like “one of us.” Reasoned compassion doesn’t require you to feel someone’s pain to treat them as valuable, but asks you to consider their well-being regardless.)

From an evolutionary perspective, selective empathy made sense: Stronger empathy for your tribe members motivated you to help them, strengthening your group’s survival, while remaining unmoved by enemy suffering prevented risky behavior that might compromise your group. But Rein points out that in today’s diverse societies, this programming is problematic because we constantly encounter people who are different from ourselves. Living in a globalized, multicultural world requires us to extend empathy more broadly to people from different backgrounds, cultures, and belief systems. When we don’t, we struggle to connect across differences, reinforcing isolation and division.

(Shortform note: Jonathan Haidt argues in The Righteous Mind that our brains go a step further than simply feeling less empathy for people outside our group: In-group loyalty is treated as a moral virtue in itself. Empathizing across difference is hard not just because the emotional pull is weaker, but because something in us feels it’s the right way to feel. There’s a silver lining, though. Haidt notes that group identity is deeply context-dependent: We all belong to many overlapping groups simultaneously, and who counts as an “insider” shifts depending on the situation. The more groups you belong to, the more people you’re likely to experience as fellow insiders across different contexts.)

How to Build More Connection

Rein argues that humanity faces a choice between two futures. In one direction lies increasing isolation as automation eliminates human contact and digital communication substitutes for face-to-face interaction, leading to worsening health and greater loneliness. In the other direction lies deliberate connection: choosing to show up in person, answer calls, engage strangers, maintain friendships, and extend empathy more broadly.

Rein suggests that deliberate connection is the healthiest choice: When you recognize that isolation triggers biological stress leading to inflammation and disease, convenience seems less appealing. And when you understand that your brain systematically underestimates social benefits, you can override your reluctance to choose connection over convenience. This section explores how to build more connection by understanding your own needs, overcoming mental barriers, and optimizing your interactions.

Understand Your Individual Needs

Rein writes that a good place to start is by identifying your social needs. Not everyone requires the same amount of social interaction. People exist on a spectrum from highly introverted to highly extroverted, reflecting genuine differences in how their brains process social reward. While both introverts and extroverts experience mood improvements after conversations, extroverts can tolerate more interaction before feeling drained. The key is to figure out how much connection you need to avoid the biological stress of isolation. If you’re an introvert, that might look like one meaningful conversation per week; if you’re an extrovert, it might look like a few meaningful conversations per day.

(Shortform note: In Quiet, Susan Cain agrees with Rein that the distinction between introverts and extroverts reflects genuine differences in how brains process stimulation. Extroverts show greater activity in brain regions associated with dopamine production and reward processing, which makes them more driven by novelty and external engagement: They need more social input to feel satisfied. Introverts, by contrast, are more reactive to stimulation in general, which is why social situations that energize an extrovert can genuinely drain an introvert. But thanks to what Cain calls the “Extrovert Ideal,” the message that the ideal person is bold and sociable, introverts may have trouble trusting their own assessment of what they actually need.)

To learn more about your own social needs, Rein recommends taking notes on your interactions and their effects. After socializing, write down who you were with, how long your interaction lasted, what you did, and how you felt during and after. Over time, you’ll notice patterns that reveal which types of interactions energize versus deplete you, how much recovery time you need, and how often you need to interact.

(Shortform note: Rein’s social journaling idea—tracking your interactions and noticing how they make you feel—is a self-discovery technique that shows up in career design. In Designing Your Life, Stanford professors Bill Burnett and Dave Evans recommend keeping a daily log of your activities, noting who you were with, what you were doing, and whether you felt energized or drained, then looking for patterns over time. Burnett and Evans are focused on helping you design a career and a life that makes you happy, not specifically on improving your social life—but the underlying logic is the same as Rein’s. You can’t figure out what you need by thinking about it in the abstract; you have to watch yourself in action and let the data tell you.)

Overcome Your Brain’s Mispredictions

Once you understand how much social interaction you need, the next step is learning to override your brain’s faulty predictions and question your initial resistance to connection. When you feel reluctant to answer a call, attend an event, or start a conversation, remember: Research shows you’re almost certainly underestimating how much you’ll enjoy the interaction and overestimating the likelihood of awkwardness or rejection. Your hesitation reflects brain biases calibrated for ancient tribal life, not an accurate assessment of modern reality. This doesn’t mean you should ignore genuine tiredness or energy depletion. But it does mean distinguishing between true exhaustion and your brain’s default caution about social risk.

(Shortform note: The finding that we mispredict social outcomes emerges from a broader flaw in human cognition. In Stumbling on Happiness, Daniel Gilbert argues that your brain routinely generates inaccurate visions of how you’ll feel in the future, and, crucially, you have no idea it’s doing this. When you picture a phone call or a party in your mind, your brain borrows from your present emotional state and pastes it onto the imagined scenario. Feeling tired or flat right now? Your mental preview of the party will feel tired and flat, too—even though the real experience almost certainly won’t. The good news is that you can learn to treat your pre-event dread less like accurate self-knowledge and more like a weather forecast generated by the wrong model.)

Rein explains that beyond recognizing your brain’s faulty predictions, you can take concrete steps to increase your social confidence. You’ll feel more confident if you feel likable, and likability is within your control: Make eye contact during conversations. Smile. Ask follow-up questions to show that you’re interested in what others are saying. Put your phone away during in-person interactions. Finally, mirror the other person’s body language. These behaviors work because they signal to others that you’re engaged, interested, and safe to connect with.

Why the Tactics Rein Recommends Actually Work

There’s a reason Rein’s list leads with eye contact, posture, and smiling rather than with what to say: According to Allan and Barbara Pease in The Definitive Book of Body Language, people process what they see before they process what they hear. By the time your words arrive, the other person has already formed a preliminary impression—and your words will be evaluated inside the frame that impression creates. Get the nonverbal layer right, and your words land in fertile ground; get it wrong, and even the most thoughtful things you say will struggle to take root.

What makes this especially useful for someone trying to build more connection is that these behaviors work in two directions. They don’t just signal warmth to the other person, but also feed back into your own emotional state. Smiling, for instance, triggers a physiological response that nudges you toward feeling better. So practicing these behaviors when you’re feeling socially anxious isn’t just a performance for the other person’s benefit, but a way of shifting your own experience. The most effective version of these behaviors tends to emerge from genuine attention and curiosity, not from running through a checklist. But if you’re focused on truly listening to the person in front of you, much of this will happen on its own.

Expand Your Empathy

Another way to build more connection is by deliberately expanding your empathy. You can train yourself to feel empathy for people very different from yourself by actively searching for points of connection—like shared interests, similar life roles, and common experiences. Finding even small areas of overlap can help you feel empathy for someone your brain might otherwise categorize as an outsider. If empathy still doesn’t arise naturally, imagine substituting someone you love into their situation—this mental exercise can activate empathic responses that don’t engage automatically.

In fact, empathy isn’t as fixed as you might think. Rein’s research on MDMA (ecstasy) showed that the drug dramatically increases empathy by elevating serotonin levels in the brain, and can even restore empathic behavior in mice with autism-related genetic mutations. Similarly, psilocybin (the active compound in psychedelic mushrooms) creates what researchers call “ego dissolution”—a sense that boundaries between yourself and others dissolve, leading to feelings of unity and increased empathy. While Rein isn’t recommending you take these substances, this research demonstrates that empathy operates through brain chemistry that can potentially be strengthened through deliberate practice and intention, not just through drugs.

Empathy Starts With Attention

Rein’s claim that empathy can be strengthened through deliberate practice sounds hopeful, but how would this actually work? In Focus, Daniel Goleman offers an answer: Empathy is fundamentally a form of attention. You can’t feel what another person is feeling if you aren’t paying close attention to them—which means that, like attention itself, empathy is a trainable skill rather than a fixed trait you either have or don’t. Goleman describes a technique he calls “behavioral empathy”: If the feeling of empathy doesn’t arise naturally, try performing the actions of empathy first—making eye contact, mirroring body language, asking questions—and the feeling tends to follow.

As Rein argues, research into psychedelics also supports the idea that you can purposefully cultivate empathy. In How to Change Your Mind, Michael Pollan explains that psilocybin works by suppressing the brain's default mode network (DMN), the cluster of brain regions responsible for maintaining your sense of being someone separate from others. When it quiets down, the boundary between self and other becomes more permeable, which is why people in that state so often describe feelings of connection and unity they don’t normally access. This suggests that the self/other boundary isn’t fixed neurology—it’s a brain state, and brain states can shift.

Outside of psychedelics, there are other ways of quieting the DMN—for example, meditation, awe-inspiring experiences (like seeing natural wonders), and music have been shown to dampen activity in those parts of the brain. This may help explain why engaging in meditation, experiencing awe, and listening to music together can help us better connect with others. So, if you want to enhance your capacity for empathy without psychedelics, these activities promise a path forward.

Choose Higher-Quality Interactions

Rein says another strategy is prioritizing higher-quality forms of interaction. Remember that different communication formats provide different levels of social reward: In-person contact activates your brain’s social systems most fully, followed by video calls, then phone conversations, and finally text messaging. So, to get the maximum benefits of connection, upgrade your interactions as often as possible. If you were going to text, call instead. Likewise, if you were going to get your groceries delivered, go to the store instead. Each step up the ladder preserves more of the social cues your brain evolved to process—facial expressions, vocal tone, body language, eye contact—making the interaction more satisfying.

(Shortform note: Rein's advice to choose the grocery store over the delivery app sounds simple. But if you find yourself consistently defaulting to convenience, that may be less about laziness than about a much larger pattern. In The Comfort Crisis, Michael Easter argues that modern life has engineered away an entire category of mild physical and social challenge: the effort of an errand or the low-level friction of navigating the world. He argues that when we eliminate these challenges, we also forfeit the confidence that comes from discovering we can handle more than we thought, and the resilience that friction helps us build. Easter suggests this is linked to anxiety and depression, and rebuilding confidence starts with embracing inconvenience.)

Rein also argues that when online interaction is necessary or just practical, small adjustments can improve the quality. For example, you can make texting more socially rewarding by using emojis. Research shows viewing emojis triggers neural responses similar to viewing facial expressions, partially restoring your brain’s ability to understand emotional context.

(Shortform note: Rein’s advice to use emojis assumes that a smiling or frowning face reliably signals the emotion behind it. But Lisa Feldman Barrett complicates this in How Emotions Are Made. Barrett argues that facial expressions don’t map neatly onto emotions: A grimace might mean anger, disgust, surprise, or discomfort, and the same emotion can look entirely different across people and cultures. We don’t decode emotions from faces so much as construct interpretations using context, relationship, and past experience. The same is true for their digital stand-ins. The practical implication: If you want your emotion to land, the responsibility is on you to be explicit, perhaps saying “I'm being playful here” or “I genuinely appreciate this.”)

Prioritize Deep Bonds

Finally, to meet your connection needs, Rein advises prioritizing certain close relationships. He explains that romantic partnerships and parent-child bonds activate the social reward system more intensely than casual friendships, flooding your system with oxytocin that reduces inflammation, suppresses stress, promotes healing, and protects neurons. This doesn’t mean you must be in a romantic relationship to be healthy—close friendships also trigger oxytocin and provide benefits. But it does highlight that deep, intimate bonds where you experience frequent physical affection and emotional vulnerability offer particularly powerful rewards for your brain and body.

It’s Not About the Label—It’s About the Security

Rein tells us that deep bonds are more neurochemically powerful than casual ones, but what actually makes a bond “deep”? Research on attachment theory suggests it has less to do with romantic status and more to do with consistency and safety. According to Amir Levine and Rachel Heller in Attached, the health benefits Rein describes come from having someone who reliably shows up for you—feeling securely connected calms your nervous system as it stops running the low-level threat response that isolation triggers. An unstable relationship, by contrast, creates the same stress that Rein attributes to isolation, even though you’re not alone.

Biology supports this. John and Julie Gottman’s book The Love Prescription shows that physical affection releases oxytocin and shifts your body into a healing state, while touch deprivation chronically elevates cortisol, producing the inflammation Rein associates with isolation. A 20-second hug with anyone you’re close to delivers a measurable oxytocin dose; holding a loved one’s hand during a stressful moment reduces fear and pain. The implication is the same whether you’re thinking about a romantic partner, a best friend, or a sibling: Your nervous system responds to security and physical presence, not the category of the relationship.

Rein adds that even relationships with pets can help meet your need for connection, especially if you struggle with human relationships or live alone. When dogs and their owners make eye contact, both experience oxytocin surges—the same bonding hormone released during human interaction. Dog owners show lower blood pressure, reduced cortisol levels, and decreased cardiovascular risk compared to non-owners, and the companionship buffers stress responses. That said, it’s worth noting that pets can’t fully substitute for human contact.

Why Dogs Soothe and Cats Invigorate

The relationship between pets and health has generated decades of research—and some surprising results. Among the most striking: A 2015 study found that when dogs and their owners hold eye contact, oxytocin rises in both of them at once, but this doesn’t happen when researchers run the same experiment with wolves raised by humans. This suggests that through domestication, dogs seem to have developed a sensitivity to human gaze that other canines lack.

What if you’re more of a cat person? A 2023 study of cat owners interacting with their animals at home found that heart rates actually went up, not down—which sounds alarming until you consider the researchers’ interpretation: They suggested this reflects a kind of positive, energizing arousal rather than threat-based stress, the physiological signature of engagement and pleasure rather than danger. The upshot is that dogs and cats seem to act on their owners in meaningfully different ways—one calming, one invigorating—which may explain why both types of pet owners experience real health benefits, just perhaps of different kinds.