Tit for tat is a strategy which, according to game theory, is the most effective choice for iterated games based on mutual cooperation or defection. Both players benefit if they cooperate, but one benefits and the other loses out if only they defect, and both lose out to a lesser extent if they simultaneously defect. As abstract as such games sound, they have important implications for understanding everything from group selection in biology to cooperation in economics.
Under tit for tat, a player will begin by cooperating, then in subsequent iterations will replicate whatever their opponent did last time. So if their initial cooperation is punished with defection, they will then reciprocate in kind. In games that are not iterated and only consist of a single round, defection is thought to be the best strategy.
Tit for tat was codified as a game theory strategy by mathematical psychologist Anatol Rapoport, but it builds upon our instinctual notions of reciprocity. It teaches us that our best option when dealing with other people we cannot trust entirely is to reciprocate their choices. Seeing as we can rarely place full trust in anyone, especially if they stand to gain by screwing us over, we lean toward tit for tat. In general, we view this as fair and just. If someone helps us, we’re quite happy to assist them the next time they need help. But if they ignore our plight when we need help, we’re highly unlikely to care in the inverse situation. For this reason, evolution tends to select for cooperative behavior in groups—it benefits everyone in the long run.
However, straightforward tit for tat is not as effective as the strategy known as tit for tat with forgiveness. This strategy involves occasionally cooperating in the face of defection. It is easy for two opponents to get stuck in a cycle of mutual defection from which they cannot escape unless and until one decides to cooperate. If both are using tit for tat, a cycle of mutual cooperation will then commence.
Life is an iterative and compounding game. In the words of Peter Kaufman, it pays to “go positive and go first.” Also, remember that people make mistakes. Assuming there is no maliciousness, it pays to forgive.
This article is an excerpt from the bestselling book The Great Mental Models Volume 2: Physics, Chemistry and Biology