When someone has wronged or hurt them

Foul play.

When some one is extremely hurt it make you do funny things.They say revenge is sweet and sometimes thats true!

Disrespect (of themselves or their beliefs)

When some one tried my temper or teased me.

When someone is wronged and cannot see justice served. That is why societies have legal systems, whereby justice is dealt out on behalf of a complainant. If someone cannot see that the penalty for the crime is sufficient, however, they may take things into their own hands.

A lack of "emotional intelligence" allowing passion to overwhelm reason.

hell has no fury as someone scorned. revenge is reaction to being hurt.

I can only really base my answer on my own experiences and the experiences I've seen others have. Revenge is something I don't seek often, as I would rather forgive. However, there was a time when I'd put my whole and absolute trust in someone and he knew all along that I trusted every word he said, then, he turned around and lied to me, and I found out. That hurt a lot and created a wound that could only be explained in English if there were only more words, but since there isn't, it makes it that much harder to define. This in turn creates hatred and a want to get back at him for how he treated me. Up to that point, he had my back. Since he broke my trust, I tried to ruin his life. I hated his next girlfriend. Tried to hurt him like he'd hurt me. Then, I learned from my mistake. I learned that my reaction made me twice as bad. I forgave them both and they both forgave me, and we're all friends again. This whole hatred thing made us closer. But yeah, I'd say, when you feel wronged or hurt or angry at something or with someone.. those are a few huge things that could fuel revenge. Revenge isn't that fun, though. It kills you inside. At least, it did for me. Only, then, I wouldn't admit it.. because it's what I wanted.