We're all products of our pasts, shaped and molded by the ideas of those around us. Many wish they had a chance to change their past, but you wouldn't stand before someone stating such if you could change your bygones, or would you? Did your past events really leave such an outstanding negative effect upon your psyche, or has your mind refused to look at the positives from a horrible happening. I realize you can't break it down into just two opposing statements, the amount of persective views are almost infinite.
If you want to modify the perception of yourself then first peer within and alter your thoughts, put yourself in the shoes of another and view the diamond for all of it's facets.