Self-Discipline means self-control. It is getting yourself to do what you really want to do, rather than being tossed around by your feelings like a leaf in the wind. You don't lose control of yourself when you feel hurt or angry, but decide how you are going to talk and what you are going to do. With self-discipline, you take charge of yourself.
When you practice self-discipline, you are controlling your own behavior so others don't have to. Self-discipline brings freedom. You get things done efficiently and have order in your life. Without self-discipline, we procrastinate. We eat things we shouldn't. We lose control of our emotions. Then people feel hurt. With self-discipline, life is more peaceful.