Tit For Tat
Farnam Street (Shane Parrish), after Anatol Rapoport · 2022
"In repeated (iterated) games, the most effective strategy is tit for tat: cooperate first, then simply mirror whatever your counterpart did last time — ideally with occasional forgiveness built in to escape cycles of mutual retaliation."
Under tit for tat, a player starts by cooperating, then in every later round simply repeats whatever their counterpart did in the previous round — reciprocating cooperation with cooperation and defection with defection. In a single, one-shot interaction (not repeated), game theory suggests defection is actually the better strategy, since there's no future round in which reciprocity could be rewarded or punished.
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Prisoner's Dilemma: What Game Are You Playing?
"The Prisoner's Dilemma shows that individually rational self-interest can produce a jointly worse outcome for everyone — but when the same game repeats indefinitely with an unknown end point, cooperation becomes far more likely to emerge and persist."