>Suppose someone comes to me and says, "Give me five dollars, or I'll use my magic powers from outside the Matrix to run a Turing machine that simulates and kills 3^^^^3 people.

It was introduced to point out a place where the currently-best "decision theory" produces a seemingly-wrong recommended action in the hope that someone might come up with a better decision theory or alternatively to explain why the seemingly-wrong recommendation is actually right. A "decision theory" is a recipe for acting in the face of uncertainty that is precisely stated enough that it might eventually serve as the basis of a computer program.