The prisoner's dilemma is a concept in game theory which is used to illustrate a variety of situations. The concept is also sometimes utilized in fields like psychology and philosophy, when people want to examine why people act in the ways that they do. Credit for the development of the prisoner's dilemma is generally given to a pair of RAND researchers, Merrill Flood and Melvin Dresher, who worked in the 1950s. Albert W. Tucker refined the idea, and christened the concept the “prisoner's dilemma.”
Classically, the prisoner's dilemma is presented as a situation involving two prisoners, A and B, who are taken into custody for a crime. The police are aware that evidence is insufficient, so the prisoners are separated and approached individually. Each prisoner is told that if he or she speaks and turns the other prisoner in while that prisoner remains silent, the talkative prisoner will go free, while the silent prisoner will do jail time. If both prisoners speak up, they will both do some jail time, although the sentence would be shorter than that for a prisoner who remained silent while another spoke, and if both prisoners remain silent, they will each be given a very short prison sentence.
Because of the way in which the prisoner's dilemma is set up, people quickly come to the conclusion that defecting and turning the other prisoner in is the best way to respond to the situation. By remaining silent, a prisoner runs the risk of being hit with a long sentence while the other prisoner walks. By speaking, a prisoner can hope that the other prisoner stays silent, in which case he or she goes free. Of course, when both prisoners speak, they both get some jail time, but the risk of remaining silent is perceived as far greater than the risk of speaking.
As a thought experiment, the prisoner's dilemma is very interesting, and some psychology classes play a real-world version to show students how it works. It plays on the idea that people caught in challenging situations usually try to guess what other people will do. In the case of the prisoner's dilemma, the prisoners find themselves wondering whether the other prisoner will cooperate and remain silent, or decide to betray in the hopes of walking free.
If a prisoner assumes that the partner is trustworthy and will remain silent, speaking up is the best response in terms of self preservation, because there is a chance of walking. The prisoner might also assume that the partner has come to the same conclusion, in which case speaking up to avoid an even longer prison sentence becomes vital, and both prisoners lose out.
Many people use the prisoner's dilemma to show how situations can escalate through a series of seemingly rational options. For example, people stuck in dense traffic often choose to take selfish actions in the hopes of getting ahead, rather than cooperating with the collective. As a result, gridlock often emerges, with everyone losing in the situation.