“The real bittersweet aspect is young adulthood begins with all this time for friendship, and friendship just having this exuberant, profound importance for figuring out who you are and what’s next,” Rawlins says. “And you find at the end of young adulthood, now you don’t have time for the very people who helped you make all these decisions.”

The time is poured, largely, into jobs and families. Not everyone gets married or has kids, of course, but even those who stay single are likely to see their friendships affected by others’ couplings. “The largest drop-off in friends in the life course occurs when people get married,” Rawlins says. “And that’s kind of ironic, because at the [wedding], people invite both of their sets of friends, so it’s kind of this last wonderful and dramatic gathering of both people’s friends, but then it drops off.”

In a set of interviews he did in 1994 with middle-aged Americans about their friendships, Rawlins wrote that, “an almost tangible irony permeated these adults discussions of close or ‘real’ friendship.” They defined friendship as “being there” for each other, but reported that they rarely had time to spend with their most valued friends, whether because of circumstances, or through the age-old problem of good intentions and bad follow-through: “Friends who lived within striking distance of each other found that… scheduling opportunities to spend or share some time together was essential,” Rawlins writes. “Several mentioned, however, that these occasions often were talked about more than they were accomplished.”