The Prisoner's Dilemma is a favorite example in the game theory and social sciences that shows why co-operation is difficult to achieve even when it is mutually beneficial.
The base thesis behind the prisoner's dilemma is two prisoners having been arrested for the same offence and being held in different cells.
The ground rules are that if a prisoner confesses while his fellow remains silent, the prosecutor will drop major charges against the one who confessed.
If both prisoners remain silent, the prosecutor will have to settle for token sentences on firearms possession charges resulting in only a light sentence.
Both prisoners are not allowed to communicate with each other and they won't find out about each other's decision until they have made a decision.
Each prisoner has the following two options:
[B] say nothing
There are three possible outcomes to what the prisoners will do at interrogation.
One could confess and agree to testify against the other as state witness receiving no sentence while his fellow prisoner receives a heavy sentence.
They can both say nothing and may be lucky and get light sentences or even be let off, owing to lack of firm evidence.
Or they may both confess and probably get lighter individual sentences than one would have received had he said nothing and the other had testified against him.
The prisoner's dilemma
The dilemma both are faced with is that it is better for them to confess, UNLESS they both deny taking part in the crime.
If one prisoner thinks that the other prisoner will deny taking part, then he CONFESSES and goes with a lighter sentence or even free.The outcome where they can both say nothing would be the best for both prisoners as a group. However, the RISK that the other might confess and turn state witness is likely to encourage both to confess.
They will both get sentences that they might have avoided had they been able to co-operate in remaining silent.
Individual versus group rationality
A common view is that the prisoner's dilemma puzzle illustrates a conflict between individual and group rationality.
A group whose members pursue rational self-interest may all end up worse off than a group whose members act contrary to rational self-interest.