What the data actually shows
Sociologists who study friendship formation tend to converge on three ingredients that make friendships form almost on their own: proximity (being physically near the same people), repeated unplanned interaction (bumping into them again and again without arranging it), and settings that invite some vulnerability or self-disclosure. School, university, and to some extent early jobs supply all three by default. Most of adult life supplies none of them automatically — you have to manufacture each one deliberately.
Time is the other constraint, and there is a useful estimate of how much it takes. Research by Jeffrey Hall (2019, in the Journal of Social and Personal Relationships) suggested that, very roughly, it takes on the order of 50 hours of time together to move from acquaintance to casual friend, around 90 hours to become friends, and upward of 200 hours to become close friends. These are rough averages, not precise thresholds, and they vary a great deal by context — but they make the scale of the problem visible: those hours are abundant in a shared classroom and scarce in a calendar full of work and family obligations.
Put the two together and the difficulty is almost arithmetic. Adulthood removes the settings that used to generate unplanned hours together, and the hours themselves are exactly what closeness requires. That is why people commonly report that they have plenty of acquaintances and warmth but few new close friendships forming — they are getting some contact, just not the sustained, repeated, low-effort contact that earlier life provided for free.
Why this feels different from how it actually is
It feels like a personal failing because the contrast is so sharp. You remember a time when friends seemed to appear effortlessly, so the current effort reads as evidence that something about you has gone wrong. But the thing that changed is mostly the setting, not you — the earlier ease was a feature of being placed among the same people every day, not a skill you have since lost.
It also feels different because the work has become invisible and one-sided. As an adult you usually have to be the one to initiate, suggest a time, and follow up — repeatedly, before any closeness exists to make it feel natural. That initiating phase is awkward for almost everyone, and because it is awkward, people assume their own discomfort is unusual when in fact it is nearly universal.
And the comparison set is misleading. Other adults' established friendships, often formed years ago under those easier conditions, are highly visible, while the slow, halting process of forming new ones is private. So it can look as though everyone else has a settled circle and you are uniquely behind, when most people are quietly finding new friendship just as slow to build.
What the research says to do about it
The most consistent implication of the research is to deliberately recreate the conditions that used to be automatic: put yourself in situations with repeated, scheduled contact with the same people over time — a recurring class, team, volunteer commitment, or regular group — rather than relying on one-off events. Repetition with the same faces is what the unplanned-interaction ingredient was really providing, and it can be engineered.
Because closeness scales with accumulated hours, frequency and consistency matter more than intensity. The evidence points toward many modest, regular interactions adding up faster than occasional grand ones. Lowering the bar — a short standing catch-up, a recurring activity you would do anyway — tends to outperform waiting for the perfect plan, simply because it accumulates the hours.
Initiating and gentle escalation of openness also help. Studies of self-disclosure find that gradually sharing slightly more personal things, when reciprocated, is part of how acquaintances become friends. Being the person who suggests the next meeting is uncomfortable but is, in the data, much of what separates friendships that form from ones that quietly stall.
What the research says does not help
Waiting for friendship to happen naturally, the way it once did, rarely works in adulthood, because the conditions that made it natural are gone. Without deliberate, repeated contact, goodwill alone tends not to convert into closeness. The passive approach that worked in school is precisely the one that stalls now.
Treating it as a character problem — assuming you are bad at friendship or unlikeable — is both inaccurate and counterproductive. The research locates the difficulty in structure and time, not in personality, and the self-blame mostly adds discouragement that makes initiating even harder.
Relying on social media and online contact as a substitute for in-person, repeated interaction has weak support as a route to new close friendship. Light digital contact can maintain existing bonds, but the accumulation of shared hours and self-disclosure that builds closeness is hard to replicate through feeds and occasional messages alone.
Real numbers in context
The rough time estimates from Hall's research put the challenge in perspective: on the order of 50 hours together to become casual friends, around 90 to become friends, and 200-plus hours to become close friends. These are approximate averages that vary widely by setting and were drawn from particular samples — treat them as a sense of scale, not a formula. Their main lesson is that closeness is time-expensive, and adult schedules ration exactly that resource.
Set against this, it is worth remembering that most adults are not surrounded by large friend groups to begin with — surveys commonly find people report only a few close friends, and a meaningful share report one or none. So the slow, effortful process of building new friendship is the normal backdrop almost everyone is working against, not an experience peculiar to you.