It is bad to harbor hate and resentment toward others
John was tricked into making a fool of himself by Mark and is embarrased.
John wants to get even with Mark.
John plays a prank on Mark the following day, making Mark look foolish.
John plots a disproportionate revenge towards Mark over the course of many years before finally getting even.
John feels satisfied that he got even with his Mark and moves on.
John wastes a ton of time on plotting that could be better spent doing something more productive.