So often when we think of discipline we think in terms of rules or others driving us to do something. For the champions that is not what disciple is. The champion practices self-discipline to do what is necessary, often what is uncomfortable to do what needs to be done. There is no need for disciple to be imposed from outside. It comes from within in the form of self-disciple.
Self-disciple means that you have ownership. It is your decision, your choice. When you are in the competitive arena no coach will drive you forward, it must come from within. You must do it on your own. You must control and channel your emotions. You must draw on the hours of practice and execute what you have practiced.
Set your rules. Live by those rules. Be the best you, you can be. That takes self-disciple and control. It takes discipline to say no to distractions that will take you away from goal. The easiest way to practice self-discipline is to make the things that are necessary into habits. Creating habits alleviates the mental burden of always making decisions. Get comfortable being uncomfortable all the time ? that is the champions choice.