Punishment is the imposition of a penalty in response to an offense, and it takes many forms. “An eye for an eye” is one of the strongest human instincts—and one that can be difficult for both individuals and societies to overcome—but decades of evidence show that reciprocating harm is not always the best course of action, either for the offender or the offended. Punishment, when meted out fairly, can work to condition people not to repeat misdeeds, and threats of negative repercussions can act as powerful disincentives.
Too often, punishment is subsumed by a desire for revenge, or greatly exceeds the offense committed. Although revenge-seeking has deep roots in the human behavioral repertoire, it amplifies the injury and makes it impossible to move on. What's more, overzealous punishment is rarely an effective deterrent and may cause negative effects that extend beyond the one being punished. A hyper-reactive “tough on crime” position that favors punishment over rehabilitation, for instance, has arguably contributed to an overpopulated prison system with high rates of recidivism.
Punishment has its place—but the ability to rise above baser instincts and judge each situation objectively, and with an eye toward fairness, is one of the highest achievements of humanity and of civilization.