We cannot change the past, but we can learn from it.
travelsafar, I understand your OP, and can indeed identify and pin point moments (especially the light bulb one that made me decide to leave my first husband), and you are right when you say "so if you get it wrong first time you can not correct it."
But as I said, you can learn from it.
I also believe that you should not (to use the vernacular) beat yourself up over it, whatever "it" may be, as, returning to your first point, you cannot change it.
Forgive yourself, forgive others, move on, and try to have a positive and good heart.