There are two boxes labeled Box A and Box B, respectively. One or both will contain money. You have to choose whether to take the contents of both or just Box B. Here's the kicker. A "Predictor" who is almost-certainly infallible at predicting the future (the Predictor is maybe God or a God-like machine from the future) will have guessed beforehand which option you will choose. If the Predictor thinks you will take both, Box A will have 1,000 dollars in it, and Box B will have nothing. If the Predictor thinks you will take Box B, it will have a million dollars in it in addition to the 1,000 in Box A. So do you take both boxes, or just Box B? Edit: This is called "Newcomb's problem" btw.