If a player continued cooperation until the partner twice moved selfishly, scores were even better than if they changed to competitiveness immediately after competitiveness in the partner. It was a second chance, so to speak for the partner to be cooperative. It is clear that being naively forgiving of others' selfishness however, responding too slowly, ineffectively, or not at all to others' hurtful actions, invites further victimization. Retaliation also seemed unproductive. Remaining competitive until a partner had shown two or more instances of cooperation clearly decreases effectiveness in the relationship.
Clarity seems to be a major benefit.
If a partner knows rather than guesses what your response will be to his move, trust and cooperation becomes more likely over the longer term. Partners who react unpredictably, or according to rules too complex topredict, tend to demoralize others and decrease their own results.