The Prisoners’ Dilemma

The parable of the Prisoners’ Dilemma shows how two people can fail to cooperate with each-other, even if they would both be better off cooperating, if they don’t have the opportunity to communicate with one-another. It goes like this:

Two prisoners, Alice and Bob, have been arrested and put in separate police cells. Each prisoner is visited by a police officer who offers them the same deal: if they inform on the other, they’ll get a lighter sentence (2 years instead of 3) and the other prisoner will get a heavier sentence (5 years instead of 3).

Both prisoners know that the police are offering this deal because they don’t yet have enough evidence to get a conviction. If both prisoners refuse to talk, both will likely receive a lighter sentence of 6 months for a lesser crime.

Each prisoner knows that the other has been offered the same deal. The paradox is that while the prisoners would be better off cooperating for their mutual benefit by keeping silent, they haven’t had a chance to talk this through and come to an agreement – how can Alice be sure that Bob won’t inform on her? They may both rationally decide to talk, in which case they’ll each get a three-year sentence, when they could have had just six months.

The moral of the story? In my opinion, it’s that communication and trust are not always easy; they may require time, effort, and resources; yet this effort may be more than worthwhile if it opens up possibilities of mutually beneficial cooperation.

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