**Will you forgive your spouse if s/he has an affair with another man/woman and wanna come back to you?**

The answers to this question vary greatly in the society. Some will forgive him/her once. Others will never forgive even for the very first time. Still others will always forgive him/her because love is blind. However, if you care about te maintenance of a long-term relationship with your partner, it is highly recommended that you should let him/her know beforehand that our love will never be the same once s/he has an affair. Here is the reason why.

Before looking into this problem, we should acquire a fundamental theorem, which is known as “Folk Theorem." (because this theorem is believed and discussed but never officially published) After foraging through the Internet, I found the definition of Wikipedia the most well-rounded. (as usually. Thanks “God" there is open source!)

In game theory,

folk theoremsare a class of theorems which imply that in repeated games,any outcome is a feasible solution concept, if under that outcome the players’ minimax conditions are satisfied.The minimax condition states that a player will minimize the maximum possible loss which he could face in the game. An outcome is said to be feasible if it satisfies this condition for each player of the game. A repeated game is one in which there is not necessarily a final move, but rather, there is a sequence of rounds, during which the player may gather information and choose moves.

In other words,

the players need only adhere to an almost grim trigger strategy (A grim trigger strategy is a strategy which punishes an opponent for any deviation from some certain behavior. )under which any deviation from the strategy which will bring about the intended outcome is punished to a degree such that any gains made by the deviator on account of the deviation are exactly cancelled out. Thus, there is no advantage to any player for deviating from the course which will bring out the intended, and arbitrary outcome, and the game will proceed in exactly the manner to bring about that outcome.

A motto from this theorem is that a long-term cooperation is retainable if players threaten to punish deviators to the extent that the gains from the cooperation will be totally canceled out. That is, once the other player defects, the player should force the other’s gain to his reservation payoff–the largest payoff he can guarantee receiving no matter what the other player do. Applied in our love story, the theorem tells lovers to threaten your partner that you will be heartbroken once you have an affair even for only one night!

A problem with this analysis lies in the likely decrease of your partner’s payoff in cooperation with you. However, if s/he comes back to you again. This act may suggest that the payoff of cooperating with you remains indifferent.

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