Perplexed:

My own solution is to shift my terminal values to the meta level. Instead of demanding success of myself (and then feeling bad if success turns out to be unattainable) I reward myself with a gold star if I judge that I have done my best. I live my life so as to have no regrets.

Trouble is, "doing one's best" is an elusive concept. Sure, there are situations where you have a clear goal and see a clear plan of action for how to give your best shot at it, so if you fail despite following it, you can still give yourself a gold star for doing your best. But at least in my experience, typical mistakes and failures in life are nothing like that. Truly critical problems and dilemmas usually can't be tackled with such a clear and accurate model of reality.

When I reflect on my own mistakes and failures, most of them were due to misunderstandings of the situation and errors of judgment that seem clear in retrospect and would have been avoided by someone more shrewd and knowledgeable in the same situations, but were completely beyond my mental and intellectual powers at the time. Others were due to lack of willpower that seems like "failure to do my best" in retrospect, but back at the time, the necessary level of willpower seemed (and probably was) impossible. In both sorts of situations, I did "give my best" in a very real sense, since nothing else could have been expected from me. But this leads to a tautological interpretation of "doing one's best" that would imply that nobody should ever have regrets about anything.