Box of delight

As external conditions change, it becomes tougher to meet the three conditions that sociologists since the 1950s have considered crucial to making close friends: proximity; repeated, unplanned interactions; and a setting that encourages people to let their guard down and confide in each other, said Rebecca G. Adams, a professor of sociology and gerontology at the University of North Carolina at Greensboro. This is why so many people meet their lifelong friends in college, she added.

No matter how many friends you make, a sense of fatalism can creep in: the period for making B.F.F.’s, the way you did in your teens or early 20s, is pretty much over. It’s time to resign yourself to situational friends: K.O.F.’s (kind of friends) — for now.

But often, people realize how much they have neglected to restock their pool of friends only when they encounter a big life event, like a move, say, or a divorce.