It's mostly limited to this site, and I don't know how much that exact wording is used, but it refers to things like Newcomb's problem, where you can get some benefit from what you do, but you're not actually causing it.
I should add that when I told Manfred, I didn't understand, it was more that I didn't understand how it applied to that situation.
I'm familiar with the concept of an acausal trade. But I don't understand how it applies to the situation of playing Prisoner's Dilemma with your cousins.
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