People plotting revenge experience heightened activity in the brain's reward center.
You've picked the perfect project for your sixth-grade science fair and tell your best friend Mary all about it. When it's your turn to claim the cabbage pH indicator experiment, your teacher informs you that Mary has already called it. Traitor! What do you do? Your brain is probably yelling at you to seek revenge.
Let's say you did sabotage Mary's cabbage experiment—would it make you feel any better? At the moment, it certainly would—a 2004 study in the journal Science found that people plotting revenge experienced heightened activity in the brain's reward center. According to the study, "people derive satisfaction from punishing norm violations." In a 2016 study in the Journal of Personality and Social Psychology, researchers found that people who feel wronged (specifically, social rejection) feel the need to improve their gloomy mood by any means necessary. That includes "retaliatory aggression," in this case sticking pins in a voodoo doll. And, guess what? Aggression works! Those who retaliated felt just as good as those who hadn't been rejected in the first place.
This could explain why some people seek out conflict—the aggression they get to unleash feels rewarding. However, it's important to note that these studies don't always account for long-term happiness. Many researchers have found that initial catharsis doesn't stick. Once the initial high of retaliation ends, the avengers' wounds still need healing.
But, there are instances when revenge is sweet. A 2010 study showed that vengeance was gratifying if the offender knew the reason they were being punished and admitted that they deserved it. German psychological scientist Mario Gollwitzer elaborates: "The finding that it is the offender's recognizing of his wrongdoing that makes revenge sweet seems to suggest that—from the avenger's perspective—revenge entails a message. If the message is not delivered, it cannot re-establish justice."