Regret for what you didn't do, for what you didn't try, for what you didn't pursue, or for what you wish you had done is more painful than any perceived failure.
Failure only happens when you quit. Everything else that you attempt and don't succeed at can be seen as a learning experience. "This didn't work, let's try that." "I know not to do that again." Seek the lesson and never see it as a failure. It's not a failure. It's a valuable experience that you can learn from. Learn the lesson and move on.
Regret is sorrow, it can be painful, it may be for something you don't get another chance at. If you go for it and don't succeed, that's ok. But if you don't go for it, you'll never know what could have been. Lost moments, lost time, don't live life with regrets. Cherish every moment, embrace every moment. Live life to the fullest. Always do your best and never have regrets.
Go after what you want. Stretch yourself. Don't let fear, anyone or anything get in the way of you going after what you really want. Then you can live with no regret.