Subjects who know the actual answer to a question assign much lower probabilities they "would have" guessed for that answer, compared to subjects who must guess without knowing the answer.
( :p )
Seriously thou, maybe something from physics or math?
EDIT: Or something about sleep. Or some anti akrasia method. Or the schedule of some technological progression...
Having started of like this already, lets just make this the post that people can comment rambling lists of random subjects for inspiration?
EDIT2: For a specific math one that seems easy maybe a logarithmic curve that the value further along has to be guessed for? Might backfire if the reader is to good at math thou.
(Also, I just realized where I am and who made the request. Eeep! don't downvote me into oblivion please...)
I'm writing the section of the rationality book dealing with hindsight bias, and I'd like to write my own, less racially charged and less America-specific, version of the Hindsight Devalues Science example - in the original, facts like "Better educated soldiers suffered more adjustment problems than less educated soldiers. (Intellectuals were less prepared for battle stresses than street-smart people.)" which is actually an inverted version of the truth, that still sounds plausible enough that people will try to explain it even though it's wrong.
I'm looking for facts that are experimentally verified and invertible, i.e., I can give five examples that are the opposite of the usual results without people catching on.
Divia (today's writing assistant) has suggested facts about marriage and facts about happiness as possible sources of examples, but neither of us can think of a good set of facts offhand and Googling didn't help me much. Five related facts would be nice, but failing that I'll just take five facts. My own brain just seems to be very bad at answering this kind of query for some reason; I literally can't think of five things I know.
(Note also that I have a general policy of keeping anything related to religion out of the rationality book - that there be no mention of it whatsoever.)