The prisoner's dilemma (revised table)

Axelrod found tournament participants adopted one of three general approaches to their strategies:

1. Always defect (the "best" strategy for a one-off encounter).

2. Always cooperate (and run the risk of losing out if your opponent decides to defect), or

3. Behave randomly (keep your opponent confused by cooperating or reneging unpredictably).

The simple strategy that led to the best overall outcome was called Tit for Tat. Tit for Tat always started by cooperating and then mimicked whatever its opponent did the last time they met. If an opponent reneges, Tit for Tat reneges on the next occasion. If the opponent cooperates, Tit for Tat cooperates in return.

The tournament also trialled several variations of Tit for Tat. Tit for Two Tats is a charitable strategy. It almost always cooperates and only retaliates when the opponent has defected twice in a row. Two Tits for Tat, on the other hand, is a severe strategy that punishes every defection with two of its own. Neither of these two variations did as well as the simple version of Tit for Tat.

One reason the Tit for Tat strategy is so successful is its consistency. Opponents learn quickly how it will behave. This does not mean that Tit for Tat is always the "best" strategy. Because Tit for Tat imitates what the opponent did last, it performs poorly when facing an opponent who always defects. To foster good outcomes, players must adopt a strategy that works with what their opponent is doing.

Like much of social life, the relations among countries require both cooperation and competition. All states put their interests first, but sometimes a nation's interests may best be protected by advancing the interests of others. For example, less hoarding and more sharing of Covid-19 vaccines would have slowed the rapid spread of Covid-19, saving lives not only in poorer countries but also by reducing the risk of new variants which affect all countries, including wealthy ones.

Although all tournament players had a chance to refine their strategies, a repeat of Axelrod's tournament produced exactly the same outcome. Tit for Tat was again the best strategy. Based on the two tournaments, Axelrod identified four rules for social interactions:

1. Cooperating often encourages others to do likewise. So, always start with cooperation, and continue to cooperate as long as your opponent does.

2. To discourage selfish behaviour, retaliate immediately for any unprovoked betrayal.

3. Forgive easily and return to cooperation.

4. Always be predictable so that others will know how you will respond to their behaviour.

The Prisoner's dilemma transcends politics; it is a moral rather than a legal issue. According to Axelrod, Tit for Tat won the tournaments even though it could never do better than the player it was interacting with. That is, it won by eliciting cooperation to create win-win outcomes The lesson is clear; if you want to get on in life, always start by being nice to others; forgive traitors, but don't be a pushover.