I recently wrote this for a friend who is having a rough time and having some regrets. She wishes some things were different. She regrets decisions she made. I have done both, myself.
The difference between regrets and wishes is this:
Regrets are things that you would change if you could, but you can't.
Wishes are things that you would change if you could, but need help or motivation or resources to do so.
The problem with regrets is that they make you focus on things outside your control.
Wishes are better because they encourage you to look for resources to help you achieve things that you want or need.
Regrets are poisonous because they breed feelings of inadequacy and despair.
Wishes are inspirational because they encourage you to envision yourself in a better, happier atmosphere -- and visions can lead to realities with the right mix of encouragement, motivation and luck.
Don't regret. Don't look back. Don't think about what could have/should have been.
Instead, look ahead at what can be. Look at what you wish for. The past laid the groundwork for tomorrow. Don't regret anything you did in the past, because you really don't know what joy and wonder tomorrow holds -- and tomorrow couldn't come to be if yesterday's foundation wasn't laid (with all of yesterdays joys and sorrows).
Let yesterday's regrets fade away as you journey toward tomorrow's dreams-come-true.