Why does Morrie say we need to forgive ourselves?

On the Twelfth Tuesday, Morrie pointed to a sculpture on the shelf that had been done by one of his old friends, Norman. Norman eventually moved to Chicago and when Morrie's wife had an operation, Norman never got in touch with them. Charlotte was very hurt by this and they dropped the relationship. Morrie refused to accept reconciliation with his old friend, due to pride, over the years. Morrie said just recently that Norman died of cancer and Morrie never forgave him. Not doing so pained him and was one of his biggest regrets. He told Mitch it is crucial to make peace with yourself and everyone around you.