Your options are to learn from it and do something else now or spend time regretting what you didn't do, probably regretting this time at some point in the futu

Your options are to learn from it and do something else now or spend time regretting what you didn't do, probably regretting this time at some point in the future. Personally I take the lessons and write off the time, if I ever come across a time machine I'll fix it but until then it seems silly to pump more time into regret