Except that I (and maybe others with similarly warped brains) find that my success rate in things I click "50%" for is distinctly above 50%. For much of my time playing the game I've actually got a larger fraction of "50%"s than of "60%"s right. If there were only one 50% button I'd have had no way of discovering that, which would be a shame because it clearly tells me something useful (specifically, I think, that my heuristics for guessing answers to some kinds of questions whose answers I have no explicit idea about are more effective than I thought).