The prisoner's dilemma
Mutual cooperation is best collectively. Defection is individually tempting. The structural root of trust problems.
Two prisoners interrogated separately, each offered a deal: betray your partner and you go free while they get 10 years. Stay silent and the worst either of you gets is 1 year (if both stay silent). The math says individually, betray. Collectively, both staying silent is better. Both rationally defecting leads to a worse outcome than both irrationally cooperating.
The game is the structural root of most cooperation problems in business and life. Competing companies could collectively benefit from not undercutting each other's prices. Each rationally undercuts. Both lose.
Repeated prisoner's dilemmas play out differently (Axelrod's tournaments showed that tit-for-tat strategies win). But in one-shot versions, defection dominates, which is why ongoing relationships, reputation, and enforceable contracts matter so much.
Examples in the wild
Most price wars are prisoner's dilemmas where each company would prefer if no one cut prices, but the first defector forces the rest to follow. Industry coordination (within antitrust limits) usually pays for everyone.
Activist short campaigns can be prisoner's dilemmas. The shorts collectively benefit from extending the attack; individually they'd prefer to exit first.
Many couples have an implicit prisoner's dilemma about household labour. If both cooperate (each does their share), both win. If both defect (both do less), both lose. The cooperative equilibrium requires explicit agreement.
The prisoner's dilemma is one of the mental models we apply through real cases inside the Pareto MBA — a part-time program for professionals who want to think clearly about business.