Prisoner's dilemma
prisoner dilemma · prisoners dilemma
The situation where each person is better off defecting whatever the other does, so both defect and both end up worse than if they had cooperated.
In practice
Every competitor runs the same discount because each is better off discounting whatever the others do. The industry ends with identical share and thinner margins, and no individual firm made a bad call.
The common mistake
Reading it as a story about distrust. The bad outcome arrives even when both parties are rational, informed and correctly predict each other — which is what makes it a structural problem rather than a failure of goodwill.
The prisoner's dilemma is the sharpest example of a structure that recurs everywhere: individually rational choices producing a collectively bad outcome, with nobody making a mistake.
The structure
Two people are held separately and each offered the same deal. Stay silent and, if the other also stays silent, both get a light sentence. Inform, and if the other stays silent, you go free and they get the heaviest sentence. If both inform, both get a moderate sentence.
Work it through from one side. If the other stays silent, informing is better. If the other informs, informing is better. Informing dominates whatever they do — and the same reasoning applies to them.
Both inform. Both do worse than if both had stayed silent. The bad outcome is the Nash equilibrium, and no step in the reasoning is wrong.
Why it matters
It shows that individually rational behavior does not aggregate into a good result, which undercuts a common assumption about markets and cooperation alike. The structure appears in arms races, price wars, overfishing, doping in sport, and advertising spend that every competitor must match to stand still.
What changes the outcome
Repetition. In a single round, defection dominates. Played repeatedly against the same person, cooperation can pay, because defecting today costs you their cooperation tomorrow. Robert Axelrod's tournaments in the early 1980s found that simple strategies which cooperate first and then mirror the other player performed remarkably well.
A known end. If both players know which round is last, defection unravels backward from it, which is why open-ended relationships behave differently from ones with a visible finish.
Communication and enforcement. The dilemma depends on the players being unable to make a binding agreement. Contracts, regulation and reputation all work by changing the payoffs so cooperation becomes individually rational.
In business
It explains why an industry competes away its own margin with nobody behaving irrationally, and why the escape is usually structural — long relationships, contracts, differentiation that removes the direct comparison. See positioning and the tragedy of the commons, which is the same logic with many players.
Concept web
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What is the prisoner's dilemma?
A situation where defecting is better for each person whatever the other does, so both defect and both end up worse off than if they had cooperated. No individual step in the reasoning is mistaken.
How can the prisoner's dilemma be escaped?
Through repetition, which lets future cooperation pay; through binding agreements or regulation that change the payoffs; and through reputation, which carries consequences between rounds.
Why does a known final round matter?
Because defection unravels backward from it. If both know which round is last, defection is rational there, and therefore in the round before, and so on.