D: A thought experiment which is significant in game theory.

Simplistically, suppose you and an accomplice commit a crime. Suppose you get caught, you both get taken to the police station (into separate rooms) and the police say

We can't prove you did the whole thing, but we can lay enough charges for you to do 1 year in prison. If either of you sign a confession, we will let them off, but their accomplice will do 5 years. On the other hand if both of you sign a confession you will both do 3 years.

Do you sign a confession (defect) or not sign (cooperate)? Some thought reveals that yes, it is logical to sign the confession even though both of you following the logic ensures that you both do more time than you would if you had not.

The problem is interesting because of its variations. All variations involve some number of people, each who has a choice of defection or cooperation.

A group of people are given 100,000 dollars each. They have a choice: keep it, or pool it. If they keep it it's theirs (to do with what they like). If the pool it, it goes into a common pool, and all the money in the pool gets doubled, and then the (doubled) money is shared equally amongst all the participants (regardless of whether they pooled their money or kept it).

Clearly if everyone cooperates (puts all their money into the pool) they all double their money, but each individual maximizes their personal money by defecting (keeping their money, and still getting a share of all the money which is pooled by the others).

The prisoners dilemma game gives insights into the failures of communism, the tragedy of the commons, conspiracy theories and so on.