Prisoner’s Dilemma, explained.
The Prisoner's Dilemma is a game in which each player is individually tempted to defect, yet mutual cooperation gives both a better payoff than mutual defection.
Why it happens
In the one-shot game, defection beats cooperation against either action by the other player. Repetition changes the situation: actions can affect future responses. Reciprocity can help sustain cooperation, but errors and the horizon can disrupt it.
Both players would benefit from mutual cooperation, yet each can gain by defecting in a single round. Repeated encounters make reputation and reciprocity relevant.
Read the result
Read the payoff table before comparing strategies. In repeated rounds, inspect both cumulative payoff and cooperation. A strategy's performance depends on its opponent and on the noise level, not simply on its name.
A worked example
Two partners share information
Both benefit when each shares useful information, but one can gain by withholding while receiving the other's contribution.
If both withhold, they lose the benefit they could have created together.
Repeated interaction and credible responses may change incentives, while a one-time anonymous exchange leaves the original tension intact.
OPTIONAL DEEPER DETAILGo deeper: inside the model
Inside this model
Mutual cooperation pays 3 each; mutual defection pays 1 each. A lone defector receives 5 and the cooperator 0. Tit for tat starts with cooperation, then copies the opponent's previous actual move. Noise independently flips each intended move.
Where this idea is useful
A practical use
Recurring supplier relationships can reward reliability, while short-term incentives reward cutting corners. Try how reciprocal strategies respond to mistakes.
A common misconception
“The best individual move creates the best joint outcome.”
In this payoff structure, individually dominant defection leads to a joint result worse than mutual cooperation.
What this explanation leaves out
- The payoff table and strategies are fixed. This experiment does not establish one universally best strategy; communication, forgiveness and the end of a relationship can change outcomes.
Is tit for tat always the best strategy?
No. Its results depend on opponents, payoffs, mistakes, and repetition. Noise can trigger retaliation cycles; forgiveness and other adaptations may help in some environments.
What would make cooperation worthwhile after accounting for the other player's future response?
Associated thinkers
Further reading
Explore the original research or the teaching reference behind this experiment.