I feel very little regrets. I have made some bad decisions in my life, but I made them in honesty, based on my knowledge of the time and my convictions of the time. Some have proven to be wrong, but I can't blame myself for it, since I made those descisions in sincerity.
I regret some of the things I did, namely things I did, while knowing fully well at the time of action, that it was wrong.
But, he who spends his life looking back, will never make any progress. Live life in the NOW, own This day, and not be worried about the days in the past.