[snthpy]

Your point about shared adversity is so interesting to me. I was on a "ferry" (it was really a kind of speedboat or something) from Belize to Honduras that got caught in a tropical storm. The waves were terrible, people vomiting everywhere, then the engine overheated and cut out, we had to search for life vests and eventually found some and put them on. They managed to revive the engine but the whole trip took 5 hours instead of two. It was a pretty frightening experience.

Anyway, even though I only spent a couple of hours with my fellow passengers on that boat, I felt more bonded to them than most people I met in almost a year backpacking and stayed in touch with them for a long time on Facebook.

So interesting that that's some kind of inbuilt thing. Like the OP, I also struggle making friends otherwise like which makes this more curious to me.