Resentments and grudges are natural responses to human pain and suffering, particularly if the injured believes that the act was done intentionally. However, the after effects of holding on to a resentment or a grudge can have long term impacts on your physical health, your relationships and your sanity. To be free of resentment and to let go of grudges, we must learn to let them go. Check out this article at the Mayo Clinic that sums this up nicely.