There is no use talking as if forgiveness were easy. We all know the old joke, “You’ve given up smoking once; I’ve given it up a dozen times.” In the same way I could say of a certain man, “Have I forgiven him for what he did that day? I’ve forgiven him more times than I can count.” For we find that the work of forgiveness has to be done over and over again. We forgive, we mortify our resentment; a week later some chain of thought carries us back to the original offence and we discover the old resentment blazing away as if nothing had been done about it at all. We need to forgive our brother seventy times seven not for 490 offences but for one offence.
— C. S. Lewis, Reflections on the Psalms, p. 25