I think it's important not to ruminate on our past regrets too much only because it can take away from allowing us to be in the now and enjoy our present. I mean think about it: if we spent every passing moment overthinking our past actions, we would never be able to do anything in the present, which means we'll regret that in the future, leading to more overthinking, y'know? While yes, things that have happened or that you may have done will bother you, sometimes even persist more than you can control, it's important to recognize that the past is only a fraction of your time. You still have the present and the future.
-M