Vengeance is a passion to get even. It is a hot desire to give back as much pain as someone gave you... The problem with revenge is that it never gets what it wants; it never evens the score. Fairness never comes. The chain reaction set off by every act of vengeance always takes its unhindered course. It ties both the injured and the injurer to an escalator of pain. Both are stuck on the escalator as long as parity is demanded, and the escalator never stops, never lets anyone off.
-- Lewis B. Smedes in Forgive and Forget