I often find myself saying, "What If I.... Would that change the situation? Well I learned this year let the past stay in the past. No matter how hard you try to change things in your mind and think of the ways you could of changed something or prevented something you can never change it!! So don't dwell on the past! Don't we all wish we could have a time machine and change something. I know I was thinking today" Man if I could go back in time I would have... and that could of changed everything for me. Well, I have news for you, no matter what you think you made the decision for a reason and every decision you have made in the past has lead you to today.
So remember when all you can think about is the past, that at the time that was most likely the best situation for you. Take things day by day, learn from your mistakes and strive to make the future the best it can be. Because in the end we all wish we had a time machine, but we don't. If you think about it, that one thing you could change may have made your life worse in the end. So remember you have your whole life in front of you , dont let the past determine your future!