One day, you can decide to "let go." Maybe you just "forget" or you "forgive," or you have a change of heart, you "see the light." In an instant, in a brief flash of light, the grudge and all the energy around it is released into the ether. You can actually feel a clearing, a cleansing wash over you.
You realize that the grudge was really an unnecessary block, like a big ominous, dead boulder, that you carried around inside. Sometimes it's just better to "bury the hatchet." Let go. Make Peace. Really.