What decisions have you made that you would change? And would they really have created as much of a change as you think? Those are the questions. The answers should be yes and maybe. If it's not than you probably made the right decision in the first place.
The consequences of almost all decisions, except maybe children, suicide or something that lands you in jail, can generally be changed by choosing to make a better decision now. You also have to remember that we make decisions based on what we know and who we are at the time. Thus, there really are few "bad" decisions, only ones that change your path in life, no matter how subtle. The goal is to then look at the new path, decide if is the one you want to take or is there one less rocky or more scenic (unless you want rocks and urban sprawl) and begin turning towards that path. Sometimes you may have to walk parallel to it until it merges, but with focus, faith and heart, you get on it eventually. I'm living proof. I made a lot of self-destructive decisions that not only impacted me but those around me. It took a very long time and a lot of very painful soul searching to understand what I was doing and why (not to mention some good medications), but once I began to start seeing it, I was able to look at myself in a mirror again without the horror, grief and guilt I used to see. I don't believe that any of us ever really "get there", no matter what decisions we make. That is why life has to be lived as a joyous adventure to be explored and enjoyed. So if you are not happy with the way some of your decisions turned out, it is up to you to decide is making the changes to the consequences of those decisions worth it to you. If so, you begin the soul-searching that will reveal the steps you need to take to get back on the path you want to be following. And never underestimate the power of prayer, no matter what you do or don't still believe, the stillness and quiet of unloading your soul to a higher power (yes, AA inspired, been there, done that) makes finding what you are looking for much easier.
So, the goal is to try and make understandable, well-reasoned, educated decisions, but at the times you don't, it is not the end of the world, you just have to make a decision to change your original decision.