A situation in game theory in which the best strategy from an individual perspective is the worst strategy from a collective perspective. For example, assume two diamond thieves who have acted in concert are brought in for questioning individually. Each is shown the following matrix.
Thief No. 1 Thief No. 2 Confesses Does Not Confess Confesses 6, 6 10, 1/2 Does Not Confess 1/2, 10 1, 1
If both thieves confess, they will each be sentenced to six years in prison (upper left). If thief No. 1 does not confess but thief No. 2 does confess, No. 1 will be sentenced to ten years and No. 2 will be sentenced to six months (upper right). If they both do not confess, they are each sentenced to one year (lower right). Finally, if No. 1 confesses but No. 2 does not, then No. 1 is sentenced to six months and No. 2 is sentenced to ten years. Although the best strategy collectively is not to confess in which case they are each sentenced to one year in prison the best strategy individually is to confess. If they both confess, however, they are each sentenced to six years. Confessing is the dominant strategy in a prisoner's dilemma.
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