When you know what you must do, when you must do it, and why you are doing it, things that are not in aligment with your intent seem to fall away. When you are where you intend to be, doing what you intend to do, for a goal or purpose you intend to realize, you are less likely to be knocked off your center square. Discipline calms the mind, opens the heart, and clears the path away from ego toward spirit.
When you are disciplined in your quest toward peace, joy, harmony, balance, and expansion, you are spared the confines of fear, anger, resentment, restriction, guilt, and shame. Having discipline is like doing one hundred spiritual sit-ups. It builds your spiritual strength and muscles.
Just my two cents!