Punishing bad behavior is critical for any social group. If people know that no matter how much they break the social contract you're not going to do anything about it, the social contract no longer exists. This goes for both future interactions with the person who made the transgression, as well as third parties who are aware of the transgression.
Now a rational actor would carefully evaluate the consequences of possible responses to come up with an appropriate option and if the cost of their feud were greater than the likely reward then they'ed simply let it go. While it leads to better outcomes, this is a slow and draining process.
On the other hand, a simple "eye for an eye" response will often lead to suboptimal results, particularly when the perceived sleight is very different from the actual transgression, but people still will be hesitant to mess with you all the same. While in our modern era of functional justice systems this approach is generally unnecessary, the overwhelming majority of our evolutionary history did not contain such a luxury.
Now a rational actor would carefully evaluate the consequences of possible responses to come up with an appropriate option and if the cost of their feud were greater than the likely reward then they'ed simply let it go. While it leads to better outcomes, this is a slow and draining process.
On the other hand, a simple "eye for an eye" response will often lead to suboptimal results, particularly when the perceived sleight is very different from the actual transgression, but people still will be hesitant to mess with you all the same. While in our modern era of functional justice systems this approach is generally unnecessary, the overwhelming majority of our evolutionary history did not contain such a luxury.