Self Discipline enables you to develop control over yourself. Self-Discipline begins with mastery of your thoughts, what you really are, and what you really do. Either your failures or your successes are the results of habits. We are creatures of habit, but, because we are a mind with a body, we can change our habits.
Self-discipline is perhaps the most important function in aiding you in the development and maintenance of habits of thought that enable you to fix your entire attention upon any desired purpose and to hold it there until that purpose has been attained.
If you do not control your thoughts, you do not control your deeds. Think first and act afterwards. Self-discipline is the principle by which you may voluntarily shape the patterns of your thoughts to harmonize with your goals and purposes.