Resentment is bittersweet. If we did not cherish it, we would let it go. What sort of rewards do we get from our resentment? Why do we keep score? First, it makes us feel superior to the person we resent. Also, it gives us an excuse for indulging in exquisite plots for revenge such as hurting the person by withholding our ultimate treasure — personal friendship. … Third … we chew the cud of past wrongs to enjoy the feeling of hurt that the memory kindles. … There is a sense in which we remember past wounds to hurt ourselves. [Why?] … We feel noble and worthy as the decent person who was wrongly hurt. Resentments serve a double purpose: they give us treasured pain, and they give us a chance to justify ourselves. So we get two rewards — a) neurotic pleasure, and b) religious pain. But we do, in fact, also hate resentment … It depresses us, robs us of gratitude, sneaks into other relationships.

— Lewis Smedes, from Love without Limits