I think about that a lot - sometimes I really wish life had a rewind button, sometimes I wish I could undo a decision, but then I think of all the things that wouldn't have happened, if I had taken a different route.
I regret a lot however I refuse to look back anymore. I am just looking forward and hoping for the best.
And the key word here is dwelling...since we all do it...and that's okay but not to dwell.
Learn from past mistakes rather than dwell on them. That will make you a better, more successful, and happier person.