I've never bothered to fill out a social networking profile beyond the bare minimum but if I had, then Warren Zevon, Carl Hiaasen and David Letterman would all have featured. So I knew already that the three were intertwined in real life - even though I came to each of them individually and by unconnected routes.
But reading Zevon's biography, I was surprised to see how many other people I like were also part of his life at some time. In similar vein, I'm frequently discovering that people who've become friends turn out to have a read the same obscure business book as I did years before we met.
I don't know what this means or how it happens, but it's not coincidence.