Self-blame is like worry in that it is not only useless and counter-productive but even destructive and yet some of us just seem hardwired to loop endlessly through these traps. One thing I can say, that Michael, seems to have touched on, is that at a certain point in your life it is sheer exhaustion with the burden of all that negativity directed at yourself that just makes you say, "enough." In my own life, age played a part. A huge tenet of Buddhism is compassion for oneself. It is uncomfortable. We feel the need to endlessly self-punish, to put ourselves down and see everything we do in a less than generous light. Why?
I can't really answer my own question but I do think that we live in one of the strangest times. Our culture is one of unbelievable narcissism and self-obsession and greed and yet people feel worse about themselves than ever before. We are taught to blame, but never taught how to forgive or even why we should. We live in a culture of craziness. It is a revolutionary act to face yourself in the mirror and practice acceptance for what you see. In the case of what you have "done", wrongs you feel you have committed or behavior that you are not proud of, what if you were to see those acts as your teachers rather than what defines you? I know that the things that I have done wrong in my life are the foundation for my whole moral outlook. Parents and teachers can say, "don't lie or cheat or steal", but it is simply an abstract until you do one of those things and see the pain you cause by doing so. Sometimes it takes a long time to get the lesson.
It is interesting to me that two people that I admire so deeply, Sepher and Redleader, were the first two to respond to this thread and express how difficult self-forgiveness is in their own lives. From the outside, I could say without a doubt that these are two of the finest human beings around--how can they not forgive themselves when all the good they do so clearly outweighs any pain they have caused in the past (or in the present)? The book, "When Things Fall Apart" by Pema Chodron has quite a bit of useful wisdom about learning to be compassionate towards oneself in order to be truly compassionate to others.
Michael, congratulations on your resolve to change a self-destructive pattern and your success in doing so. Thank you for starting the thread and thus, the discussion. We can all benefit from this no matter where we are or what we have done, or not done, in life so far. We are human beings, perfect in our imperfections, perfect in our ability to change and adapt and learn until the day we die. I find that very comforting and very exhilarating at the same time.