The Parable of Tit for Tat

Tit for tat is an English saying meaning “equivalent retaliation”. It is also a highly effective strategy in game theory for the iterated prisoner’s dilemma. The strategy was first introduced by Anatol Rapoport in Robert Axelrod’s two tournaments, held around 1980. Notably, it was (on both occasions) both the simplest strategy and the most successful.

Wikipedia: Tit for tat

An except from No-one makes you shop at Wal-Mart by Tom Slee p 80-82, slightly paraphrased:

The winner was to be the strategy that accumulated the most points over the tournament. The conditions for victory did not include “beating” opponents in individual games, all that mattered was the number of points scored overall. Sophistication was not the key to success: the winner was the simplest strategy, the now well-known Tit-for-Tat:

  • On the first move, co-operate.
  • On every subsequent move, play what the other player played on the previous move.

Tit-for-Tat exemplifies reciprocity. It successfully encourages, using a mixture of carrot and stick, other strategies to take part in mutually beneficial co-operation. Overall it got the most points of any strategy even though, or perhaps even because, it can never do better than any “opponent”. Instead, its success at encouraging co-operation means that games in which it plays are high-scoring.

There is no unambiguous “best strategy” for the game. Nevertheless considerable empirical evidence supports the observation that under a wide range of conditions, Tit-for-Tat and similar strategies are highly successful. Most of these successful strategies shared traits which Axelrod highlighted in his analysis:

BE NICE. Co-operating on the first move makes it possible for a mutually beneficial pattern of co-operation to be established.

BE UNEXPLOITABLE. By responding to defection with defection, Tit-for-Tat avoids being exploited by strategies designed to take advantage of overly generous opponents.

BE FORGIVING. If the opponent co-operates just once, Tit-for-Tat will forget about all previous defections. This prevents mutually destructive cycles of revenge from being established.

BE CLEAR. It’s easy to see what Tit-for-Tat is doing, making it easy for other strategies to settle into patterns of mutually beneficial co-operation.

The Parable of Tit for Tat

How to be kind, without letting others abuse your kindness? How to act with compassion and openness, when the world seems to punish these things? How to build a life of bountiful co-operation instead of endlessly competing in zero-sum games?

The parable of Tit for Tat suggests a way: be optimistic and friendly by default, but punish immediately those who harm you. Let others see clearly how you protect and care for your allies, and let them see clearly what they have to do in order to become your ally.

Let them see that you are as immovable as the bedrock. You are playing the strategy that seems best to you, and you will not be swayed from it. They cannot convince you or cajole you. They cannot change your behaviour, they can only change their own.

Is Tit for Tat morally good? Is the wrong question. It’s just a good strategy, a technique that can be used for good or for ill. But it’s interesting to note that Tit for Tat is exactly the way you should treat a child who sometimes misbehaves, or an adult who is hurting too much to fully take care of themself. Which is to say: most adults, if we’re honest.

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