“When the future of the interaction is not important enough relative to immediate gains from defection, then simply waiting for the other to defect is not such a good idea. It is important to bear in mind that TIT FOR TAT is a stable strategy only when the discount parameter, w, is high enough relative to the payoff parameters, R, S, T, and P. In particular, proposition 2 shows that if the discount parameter is not high enough and the other player is using TIT FOR TAT, a player is better off alternating defection and cooperation, or even always defecting. Therefore, if the other player is not likely to be seen again, defecting right away is better than being nice.”

TIT FOR TAT表现好是有条件的，必须和对方有长久对局的可能性。当这个可能性降低，也就意味着可能这是一次性囚徒困境，那选择背叛测试最佳的策略。

“The moral of the story is that the precise level of forgiveness that is optimal depends upon the environment. In particular, if the main danger is unending mutual recriminations, then a generous level of forgiveness is appropriate. But, if the main danger is from strategies that are good at exploiting easygoing rules, then an excess of forgiveness is costly. While the exact balance will be hard to determine in a given environment, the evidence of the tournament suggests that something approaching a one-for-one response to defection is likely to be quite efFective in a wide range of settings. Therefore it is good advice to a player to reciprocate defection as well as cooperation. ”

报复的程度是取决于所在环境（对手）是否倾向于剥削策略还是报复策略。如果是剥削的话，那就要N报还1报（N>=1)，如果是报复策略，为了防止一直持续的相互报复（冤冤相报何时了），就要那就要N报还1报（N<=1).