You know the difference between promises and memories? We break promises, memories break us.
If you allow for your past to break you, and stop you from continuing to become a better person so that you may leave some sort of impact on it, it most certainly will. Allowing yourself to be beat up by your own thoughts, mistakes, and any other decisions that you regret having made in your past can be very destructive to the rest of your life. Not being able to let go of the past can cause stress, anger, and tension to rise and build within ourselves, until we ultimately are no longer able to sustain holding everything inside, and it erupts from within us.