"PHILOSOPHICALLY SPEAKING...":

There are two boxes: Box A contains $1000 and Box B contains either a million dollars or nothing at all. You have two choices: you can take them both or you can take only Box B. But there's just one catch: a Being* that has demonstrated an extremely high rate of accuracy in predicting your choices has already predicted your choice and that prediction has determined the contents of the boxes. If the Being predicted you would take both boxes, Box B will be empty. If the Being predicted you would take only Box B, Box B will contain a million dollars. Which do you take?

Known as Newcomb's Problem, this thought experiment has bedeviled philosophers, economists, and decision theorists since it was introduced by Harvard philosopher Robert Nozick in 1969. If you think it's straightforward, you might want to read more: https://www.theguardian.com/science/alexs-adventures-in-numberland/2016/nov/28/newcombs-problem-divides-philosophers-which-side-are-you-on or http://www.slate.com/articles/arts/egghead/2002/02/thinkinginside_the_boxes.html

*can be interpreted as a genie or God, but could be something no more supernatural than an advanced Google algorithm