Successful people maintain a positive focus in life no matter what is going on around them. They stay focused on their past successes rather than their past failures, and on the next action steps they need to take to get them closer to the fulfillment of their goals rather than all the other distractions that life presents to them.
The beauty of life is, while we cannot undo what is done, we can see it, understand it, learn from it and change. So that every new moment is spent not in regret, guilt, fear or anger, but in wisdom, understanding and love.