We all have done something we're probably not proud of and coming to terms with it is probably rather difficult. Wronging someone is probably the easiest, as forgiving others is, in my opinion, easier than forgiving yourself. But making mistakes you can't revert can only fill you with regret.
We spend our time panicking over a decision already made and waste time hesitating or repeating the scenario to yourself with different outcomes. Maybe hoping for a miracle. This time used to worry and fret over something we cannot alter anymore can probably be better off used doing something else to offset it.
My personal philosophy for regret or making a mistake is simply to accept it and move on. Very lackadaisical. But I never mistake it for an excuse not to remedy a situation but something like scoring low on a test or forgetting homework, I simply not fret and work harder next time.