Tit-for-Tat is nice, retaliatory, and forgiving — a combination that quietly builds trust.
It is nice because it never betrays first, so partners learn they are safe with it. It is retaliatory because it punishes a betrayal at once, so it is never an easy mark. And it is forgiving: the moment the other side cooperates again, it returns to cooperating. The clever strategies that tried to exploit others got punished and fell behind.
