There is absolutely no benefit in focusing on things you can’t change. It causes extra suffering and limits joy. It is far easier and more beneficial to be realistic about what you can change and focus your efforts on that.
There is never anything you can do to change the past. You can and should identify past mistakes because it means you have learned from them, won’t make them again, and now have the wisdom to help others avoid them. If you realize something you’ve done to hurt others in the past, it gives you the opportunity to try to make things right. What you can do about realized mistakes and past offenses, like everything else you can do something about, lies in what you do about it today.
There are always things about the future that you can’t do anything about. However, there are also always some things about the future you can do something about. It is good to consider the future as long as it is in order to trace it back to what you need to do today to affect desired outcomes. Focusing on future events outside of what you will do today is dishonest. It will create a feedback loop of anxiety that will prevent you from doing what you actually need to do today, causing less joy and more suffering in your life than what could have been had you not selfsabotaged.
Anxiety is experienced when we confuse the things we can change with the things we can't. Anxiety comes as we incorrectly assign the feelings that come when we aren't doing what we can about the things we can change to the things we can't change. Anxiety is caused by dishonesty and a lack of faith in God, and any treatment that doesn’t address the cause will fail to relieve the symptoms. If you are anxious, you are either not doing all you can do today, or you don’t trust that God will take care of the rest. Anxiety is relieved as you correctly parse out the things you can change from the things you can't change. When you list out these things, on paper if need be, and isolate the specific actions you can take to work on the things you can change, your anxiety will end.
The only way to affect the future is by what you decide to do today. When we do everything that lies in our power to reconcile to reality as far as we understand it, we can trust in God to ensure that whatever happens from that point is exactly what he sees as absolutely necessary on the path to our greatest joy.