"Two men are each given a necktie by their respective wives as a Christmas present. Over drinks they start arguing over who has the cheaper necktie. They agree to have a wager over it. They will consult their wives and find out which necktie is more expensive. The terms of the bet are that the man with the more expensive necktie has to give it to the other as the prize.
"The first man reasons as follows: winning and losing are equally likely. If I lose, then I lose the value of my necktie. But if I win, then I win more than the value of my necktie. Therefore the wager is to my advantage. The second man can consider the wager in exactly the same way; thus, paradoxically, it seems both men have the advantage in the bet. This is obviously not possible."
Unfortunately, at least one of the men has been drinking long enough to have forgotten that he got the necktie from his mistress and not his wife, and thusly loses regardless of the outcome.
This is not to mention the fact that asking a spouse how much they spent on anything is as likely to get you an inflated number as a deflated number and you should really consider the risk of the source of your reference points.
"Let us say you are given two indistinguishable envelopes, each of which contains a positive sum of money. One envelope contains twice as much as the other. You may pick one envelope and keep whatever amount it contains. You pick one envelope at random but before you open it you are offered the possibility to take the other envelope instead."
Punch a motherfucker in the nuts, take both envelopes, and run.
It's good to think like a criminal, is all I'm saying.
EDIT: Changed that last line.