There's no difficulty in life that can't be made even worse with a little guilt, regret and the comparing of oneself to others.
My biggest regret in life is that I'm not someone else, especially when I start comparing myself to others.
But if I look closely enough I realize that there are quite a few experiences I had and things in my life today that I wouldn't have if my past been different than it was. I also realize that had my past been different, I may likely be ruminating over a whole different set of regrets.
Sometimes in order for things to change for the better, you have to create an uncomfortable vacuume. You have to burn the old forrest down so that a new and better species of trees will grow. Typically this process isn't pretty or comfortable and is often accompanied by doubt and regret.
If one looks hard enough, one can find ants at any picnic however if a person can find even one thing in their life that they wouldn't change for the world, then their life hasn't been a waste of time. Sometimes regretting the things one didn't do, is preferable to regretting things that one has done.