Tit-for-Tat

Figure WN21.9. When individuals meet each other many times, a tit-for-tat (TFT) strategy can be stable. To give a concrete example, we use the payoff matrix of Fig. 21.33. If everyone plays TFT (blue), then they always cooperate and get a payoff of 3. An individual who always defects (red) will gain a payoff of 5 on the first encounter, but if he meets the same partner again, that partner retaliates, and the defector gains only 1. The diagram shows a series of encounters between pairs of players, with their average payoff per encounter. The common TFT strategy always does better than the invading defection strategy.