I was just discussing this thread with a friend of mine and we agreed on the same thing. Taleb has a line about college being the closest thing to a natural social state in the Western world. I think our brains feel comfortable in some sort of regular, persistent social milieu, particularly one formed by close friends/family. We expect some sort of tribe to be around us. That doesn't mean some of us aren't introverts—I definitely am one—but as I get older the absence of my friend group constantly there in the background is really painful.