We should have no regrets... The past is finished. There is nothing to be gained by going over it. Whatever it gave us in the experiences it brought us was something we had to know.
My 84 year mother loses sleep over her regrets. She ponders over everything that she did wrong when she was bringing us up and she tells me at least once a week. That strikes me as strange as in other cases, she is such a strong person. It just these regrets that she can't seem to manage.