I read somewhere that holding a grudge is like taking poison and waiting for the other guy to die.
That said, I tend to be up in my own head too much generally and it's difficult for me to let some things go. I recognize that there's little to be gained by dwelling on anything overly much but thought patterns are tough to change.
I do learn from every wrong, however. As GW Bush brilliantly said, "Fool me once, shame on you. Fool me twice....uh, uh....won't get fooled again".