Anyone who positively accepts and practices the theory that spending time regretting our actions in the past is a complete waste of our time and energy, as we cannot change our past, will never fall prey to anxiety and depression caused by such negative thoughts of our past.
Ask yourself, will spending your entire life regretting your actions and decisions in the past bring peace to you? Not at all.
Did all your years of worrying and regretting bring any change to the events in your past which caused you pain? Not at all.
Realise, when you worry about the past, you are worrying about something you cannot change at all. No amount of regret will change your past in the way you want to. Understand the uselessness of worrying about something you do not have any control over.
Live in your present without regretting your past. Do it now. You will find the world around you has become more beautiful than ever.