A person who never regrets his wrongdoings is likely to repeat them.  But excessive guilt is harmful.  An important factor concerning regret is whether a person feels bad that he feels bad, or feels good about his regret….

Ask yourself, “Will my blaming myself help me improve or not?” To the degree self-blame motivates you to change for the better, it is positive.  Self-blame that prevents improvement is counterproductive and should be overcome.   When you stop feeling self-pity over your mistakes, your mind will be free to work on improvement.  ~ R’ Zelig Pliskin