(Correction please) You should never regret what you have done.

I don’t think so, and I disagree with it. Of course, you can regret what you didn’t do (if it is something special and important); but also, you can regret what you have done. People do bad and good things, and they always regret doing it. I think that you should (regret-> use “have remorse or feel guilty” here), if you have done anything that caused injury someone else, or if you have done bad things to yourself. Also, you should regret if you haven’t done something that you want to do. For example, something that wanted to do but too scared to do it.