We like to think we know what we’re talking about when we use the term. You see it on Instagram captions, scratched into notebooks, or shouted across a crowded bar. But honestly, if you sit down and try to define what are best friends in a way that actually makes sense across a whole lifetime, it gets tricky. It’s not just a person you hang out with. It’s a specific, weirdly intense psychological bond.
Think about the "Inner Ring" theory by C.S. Lewis. He talked about how humans are obsessed with getting into the "inside" of a group. A best friendship is the smallest, tightest ring possible. It's a two-person circle. It's that feeling when you look at someone and realize they’re the first person you’d call if you got arrested or if you won the lottery. Sometimes those two things happen on the same day.
The Science of the "Bestie" Bond
We can't just talk about feelings. We have to look at the brain. Robin Dunbar, an evolutionary psychologist at Oxford, is famous for "Dunbar’s Number." He argues that humans can only maintain about 150 stable relationships. But within that 150, there’s a hierarchy. At the very top, in the "support clique," there are usually only one or two people. These are your best friends.
Research published in the Journal of Social and Personal Relationships suggests it takes about 200 hours of quality time to transition from an acquaintance to a "best" friend. That’s a massive investment. You can’t fake that. You can’t shortcut it with a few "likes" on a photo. It’s the result of shared boredom, inside jokes, and probably a few arguments that felt like the end of the world at the time.
Interestingly, our brains actually start to blur the line between ourselves and our best friends. A study from the University of Virginia used fMRI scans to show that when people are under threat, their brains react the same way whether the threat is to them or to their best friend. We literally incorporate them into our sense of self. When you ask what are best friends, the neurological answer is "a part of you."
Why We Get It Wrong
Most people think a best friend is someone who is exactly like them. That's a myth. Total nonsense. Sometimes, the best dynamic is the "complementary" one. One person is the anchor; the other is the sail. If you have two anchors, you go nowhere. If you have two sails, you crash into the rocks.
And then there's the "Best Friend Forever" (BFF) lie. We’re taught that if a friendship ends, it was a failure. That’s not true. Some of the most impactful best friendships are situational. You might have a best friend in college who saw you through your worst breakups and your hardest exams. Maybe you drift apart ten years later. Does that mean they weren't your best friend? Of course not. They were the "best" for that version of you.
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Real life is messy. People move. People change their politics. People get married and disappear into a cloud of diapers and mortgage payments for five years. The hallmark of a truly deep friendship isn't that it stays the same, but that it can survive the "stretching." It’s elastic. You don't talk for six months, then you pick up right where you left off. That’s the gold standard.
The "Lowered Guard" Effect
You know that person you can be ugly around? Not just physically ugly—though wearing sweatpants with a hole in them is part of it—but emotionally ugly. You can be petty. You can be jealous. You can admit to things that would make a stranger think you’re a terrible person.
That is the core of what are best friends. It’s a safe harbor for your worst traits.
In a world where everyone is performing on LinkedIn or TikTok, having a space where you don't have to be "on" is a biological necessity. It lowers your cortisol. It literally makes you live longer. The Harvard Study of Adult Development—the longest-running study on happiness—found that the quality of our relationships is the single biggest predictor of health and longevity. Not money. Not fame. Not cholesterol levels. Just the people who actually know you.
Common Misconceptions
- They have to be your "Twin": Nope. Some of the best friendships happen between opposites.
- You have to talk every day: Absolutely not. Some "low-maintenance" best friends speak once a month but with 100% intensity.
- Jealousy isn't allowed: We’re human. You might feel a sting when your best friend gets the promotion you wanted. A real best friend acknowledges the sting and buys the champagne anyway.
Friendship in the Digital Age
Social media has complicated the definition. We’ve "gamified" friendship. We have "streaks" and "close friends" lists. But digital intimacy is often just the illusion of closeness. You can know exactly what someone ate for brunch without knowing they’ve been crying for three days.
The "Best Friend" tag has become a bit of a currency. People use it to signal status. But real best friendship is invisible. It’s the text message at 3:00 AM that says "I’m spiraling," and the response is just "I’m coming over." No hashtags. No selfies. Just presence.
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Aristotle had a famous take on this. He called it "a single soul dwelling in two bodies." He categorized friendships into three types: utility (you’re useful to me), pleasure (you’re fun to be around), and virtue (we make each other better). A best friend is that third category. They are the person who sees the person you want to be and helps you get there, even when you’re acting like the person you used to be.
How to Actually Be a Best Friend
If you want to know what are best friends, look at the effort. It’s a verb, not just a noun.
- Practice Radical Listening. Most people just wait for their turn to speak. Don't do that. Listen for the thing they aren't saying. If they say "I'm fine," but their voice drops an octave, ask again.
- Show Up for the "Small" Stuff. Everyone shows up for the funeral or the wedding. The best friend shows up when you’re moving into a fourth-floor walk-up in July or when you just need someone to sit on the couch while you fold laundry.
- The "Vault" Policy. When a best friend tells you something, it goes into the vault. It doesn't come out for "tea" with other people. It doesn't get used as leverage in an argument later. Once trust is cracked, the "best" part of the friendship is gone.
- Forgive the Fuzziness. Life gets in the way. People get depressed. People get busy. If your friend disappears for a while, don't lead with "Where have you been?" Lead with "I missed you, hope you’re okay."
The Impact on Physical Health
This isn't just "feel-good" talk. The lack of a close, "best" level friend is as dangerous to your health as smoking 15 cigarettes a day. That’s a real statistic from a meta-analysis by Julianne Holt-Lunstad at Brigham Young University.
Loneliness kills. But not just "being alone"—it’s the "lack of being known." You can be in a room full of people and be lonely. But if you have one best friend, the world becomes manageable. They act as an external nervous system. They help you regulate your emotions when your own brain is failing at the task.
Making a Best Friend as an Adult
It's harder now. When we were kids, we just asked, "Do you like dinosaurs?" and if the answer was "Yes," we were set for life. As adults, we’re guarded. We’re tired.
But the process is the same. It requires vulnerability. You have to be the first one to say, "Hey, I really value our friendship," or "I'm going through a hard time." You have to "go first." Most people are sitting around waiting for someone else to make the first move into deep friendship territory. If you want a best friend, you have to be willing to be awkward.
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It’s about "shared activities" versus "shared talk." Men often form best friendships "side-by-side"—doing things together, like playing games or working on cars. Women often form them "face-to-face"—talking through feelings. Neither is better. Both lead to the same result: a person who holds a piece of your history.
Actionable Steps to Deepen a Friendship
Don't wait for a milestone. If you have someone you think might be a best friend, or someone you want to move into that inner circle, try these things.
First, share a secret. Not a dangerous one, just something slightly vulnerable. See how they handle it. Vulnerability is the "grease" for the wheels of intimacy. If they meet your vulnerability with their own, you’re on the right track.
Second, create a ritual. It sounds cheesy, but a standing Tuesday night phone call or a yearly camping trip creates "the lore." Every friendship needs lore. You need stories that start with "Remember that time..." Without lore, you just have a contemporary.
Third, be the "Emergency Contact." Literally. Ask them if you can put them on your form at the doctor's office. It’s a small gesture, but it’s a powerful signal. It says: I trust you with my life.
Finally, learn their "language." Some people need words of affirmation. Some people just need you to bring them a coffee when they’re stressed. Figure out what makes them feel seen. A best friend is, ultimately, the person who sees you clearly and doesn't look away.
That is the simplest, and most difficult, definition of all. It’s a person who knows the "real" you—the one without the filters—and decides that person is worth sticking around for.