Living in resentment shuts down our humanity, our humane nature. Resentment is a wrench thrown into our system of good feeling and well-being. Resentment is inhibited action.
Emotions are designed to be expressed in physical action. When we assign a feeling as 'not good," "bad" and inhibit it--we wreck our guts, our wise and precious place. So good emotions and bad emotions must be expressed. There are healthy ways to express bad feelings... without hurting ourselves or others.