Well in that case it would be to the point where it would be. "Did i do my best to stop this" if yes then don't worry. if no. learn for next time. You don't have full control over everyone and everything nor do you have full control over your life. Sometimes it comes to the point where you have to realise that the one fuck up you made is worth the 100 that you do the right thing the next time. we are only human (minus the bots) and we are always put in the point where we are tested to fix our problems and if we don't then we need to not make them again. Can you be perfect? No. Can you do better in the future? Yes. Don't forget the hindsight of today is worth nothing to the change of the past but everything to the betterment of the future.

Don't be so hard on yourself.