I often think things like this:  I wonder how many people have, while vacationing in Carmel-by-the-Sea, read Barbara Tuchman's Guns of August?  I then play a little parlour game with myself, estmating as closely as I can how many people have ever done that.  Sometimes I come across a convergence of activity, place, and person (usually me, of course) that leaves me with the inescapable conclusion that I must be the first and only person ever to have done this thing in that place.  I can't think of one of those right now, but this is probably going to be a long speech, and the subject is bound to come up again.