Serendipity. This has been on my mind, too, in a different way. More soon about that. However:

One aspect that seems to matter, crucially, is that it's informal. Scheduling a hang-out (like she describes in the paper) might be nice, and tie into some of the same vibes, but it's different. There's something vitally important, and alive, when your default respiration includes a bunch of other people around. Your people.

That's what I miss most: default sociality.