Tit-For-Tat

In an iterated game of prisoner's dilemma, cooperating in a tit-for-tat approach usually results in better long-term outcomes than constant betrayal. You can start out cooperating, and thereafter follow suit with what your opponent has recently done. In these situations, you want to wait for your opponent to establish a pattern of bad behavior before you reciprocate in kind. You don't want to destroy a previously fruitful relationship based on one bad choice by your counterpart.