Do you remember that kid you didn't like in school? He/she lived for putting you down in front of your friends and classmates.
You had solid grounds to hate this person. The person f###ed with you, laughed at you, and tried to fight you on a few occasions just for being you. The anger inside you built up till you no longer saw this person as a human being.
Eventually something happened. There was a big showdown, or a some sport you beat him (or her) at. Maybe everyone was watching and you came through. Maybe it was just a clever insult. Maybe you just pushed the right (or wrong) button.
Whatever happened, the tide instantly turned! Your enemy lost it and was reduced to a pathetic fool. It happened in the "Buddy Hinton/Baby Talk" episode of the Brady Bunch. Maybe your arch rival started to become incoherent or reduced to tears. You had now won the war. But the victory was NOT as grand as you thought.
Sadness now comes over you. You're now moved and touched and even sympathetic towards this asshole who made your life hell. You begin to realize this soul had a lot of serious issues and was using you or your friend to take it all out on. You now realize it's time to stop. You even feel bad for taking those natural steps of self defense (either physical defense or emotion/reputation defense). You killed the monster and you regret it.
That's a weird feeling (and I don't know I thought of it now). That's when I know it's time to stop. When we become adults, if we do, we can pick out who needs their payback and who should be left alone. Self-Control is key. Have mercy on me and all of us.