It's bad to continue to hold a grudge.
Bob is mistreated by his boss, and he is very angry at them for this.
Bob wants decide whether to keep holding his boss's actions against them.
Bob decides to forgive his boss for mistreating him in the past.
Bob decides he will never forgive his boss for the way they treated him.
Bob is a much happier once he's let go of his anger towards his boss.
Bob never lets go of anger towards his boss and so is never happy at his workplace.