I feel regret too, there are many experiences that, when I remember them, make my heart sink and make me think "I really fucking wish I didn't do it that way".

However, the perspective I've explained keeps me from dwelling on it for too long. What's done is done, I did the only thing I could do with the information that was available. There is no point in punishing myself (unless it's to remind myself of the lesson). That's what I meant by not "believing" in regret.

That perspective often helps me get out of the self-pitying mood.