Everyone has stories of the small coincidence by which their parents met or their grandmother was saved from fire or their grandfather from the grenade, of the choice made by the most whimsical means that led to everything else, whether you're blessed or cursed or both. Trace it back far enough and this very moment in your life becomes a rare species, the result of a strange evolution, a butterfly that should already be extinct and survives by the inexplicabilities we call coincidence. The word is often used to mean the accidental but literally means to fall together. The patterns of our lives come from those things that do not drift apart but move together for a little while, like dancers.