Newcomb's Paradox is a thought experiment devised by William Newcomb in 1960.
The problem has taken on various forms over the years but the general idea(s) remain in place.
Before you are two boxes: one transparent (box 1) that always contains $1,000 and one opaque (box 2) which either contains $1,000,000 or $0. An entity, often called the Predictor, is exceptionally good at predicting people's actions, the Predictor is almost never wrong. The Predictor explains that you have two choices: take what is in both boxes, or take only what is in the opaque box, box 2.
There is a twist; the Predictor has made a prediction about what you will decide. If the prediction is that you will take both boxes, then $0 will have been placed in the opaque box. If the prediction is that you will take only the opaque box, then $1,000,000 will have been placed inside of it. By the time the game begins, the prediction has already been made and the contents of box 2 already determined.
Which box do you choose?
In a 1969 article, philosopher Robert Nozick noted that "To almost everyone, it is perfectly clear and obvious what should be done. The difficulty is that these people seem to divide almost evenly on the problem, with large numbers thinking that the opposing half is just being silly."
To this day there is much disagreement on the best strategy.