The stackoverflow difference is that you have more than one "life". (I used to be downvoted to hell on the programming suboverflow, for what reasons ever, and thus thought it was a realistic possibility to get booted there. Frankly, I don't even know if that is possible at all, or if my account counts global for all subs.)

Rumsfelds Theorem (there are known unknowns, and unknown unknowns) immediately springs to mind. Example: No amount of search could have led me, an amateur, to "Burnside obstruction to the Montesinos-Nakanishi 3-move conjecture" (only sheer dumb luck and the fact that he's the P of HOMFLYPT). Hey, couldn't he named the paper "Reddmanns skein relation sucks because the recursion won't get started for complicated knots"? :-) And thus I'm deeply indebted for any reference MO digs up for me. Even if I don't understand a word of it (which is likely :-)