Why do we insist on fretting over the things we can't change? Worrying about the things that have already happened? Regretting the things that are left in our past?
Rather than focusing on our future, it's like we're programmed to worry about our past.We end up spending so much time, reliving our past and waiting for the future when we can move on, that we forget to live in a way that will allow us to grow and prosper as individuals. Every day, every minute, every second we spend stuck in the past is an opportunity we are missing out on for the future.
So stop it. Stop thinking about what you would have done and questioning the way things could have panned out if you had done such and such different. And most importantly, stop blaming yourself for any mishaps that might have occurred. If you put in half the amount of effort to make the best out of each day as you do looking back on the "what ifs," you might find yourself at a better place now that you had ever been before.