I do that. partly it comes from my older brother always saying to me "oh I knew that" whenever I said anything, now of course I realize he was lying liar pants on fire, but it made me rush thru and prove my point cos he plain just didn't want to listen to me; but it also left me with the conviction that yes everybody else knew exactly what I was always talking about, that I was just stating the obvious - which as it turns out is so not true, but who knew?