From an analysis of the 3-million choices made in the second Prisoner's Dilemma competition, four features of the winning strategy TIT FOR TAT emerged:
1. Never be the first to defect
2. Retaliate only after your partner has defected
3. Be prepared to forgive after carrying out just one act of retaliation
4. Adopt this strategy only if the probability of meeting the same player again exceeds 2/3.