To pull in another Shakespeare reference, when teaching Twelfth Night, we often discuss whether or not Sir Toby and Maria (as well as the incompetent Sir Andrew) are justified in seeking revenge on Malvolio when he disrupts the "party atmosphere" in Olivia's house of mourning. We often fall into the revenge for a wrongdoing, which stems another act of revenge, which continues the cycle, up until someone steps up to the plate and becomes the better person. We do an exercise when we take a seemingly insignificant action (i.e. breaking someone's favorite pencil) and create a chain of events to illustrate how revenge can get out of hand.
I also truly believe in karma. . .my dad was a big proponant of that idea and while we sometimes wanted to get someone back, it seemed less fate-tempting to just forgive and go on.
Many things can cause people to try to seek revenge on others: jealousy, anger, hurt, feeling slighted or taken advantage of, etc. I think just about everyone at one time or another has either thought of getting revenge on someone who has hurt them or has actually done something to try to get revenge.
Personally, I don't think revenge ever works. I'm a firm believer in something called "karma" and as I've grown older, I've realized the best "revenge" is karma. People reap what they sow, meaning if people do something bad or a succession of bad things, they WILL get that back in a negative way sometime in the future. It may be years down the road, but doing bad things always comes back to bite people in the rear-end, so to speak!