“Resentment is like taking poison and hoping that someone else will die.”
Helen Garner • Helen Garner on Happiness: ‘It’s Taken Me 80 Years to Figure Out It’s Not a Tranquil, Sunlit Realm’
resentment does nothing to change the person we resent. Nor does it resolve conflict. Instead of freeing us from the wrongs of others, resentment invites those people and incidents to dominate our thinking—a kind of emotional bondage.
Sharon Salzberg • Real Change: Mindfulness to Heal Ourselves and the World
Resentment is like drinking poison and waiting for the other person to die.
– Carrie Fisher

As you have probably heard, holding on to resentments is like drinking poison and expecting the other person to die.