" In fact, delayed gratification is another way you can define self-discipline because it takes you through the same process to the same outcome. You suffer now for a specific outcome later, and doing so requires mental fortitude, pushing your boundaries, and doing more than you thought you could. Whenever you seek to delay gratification, you use self-discipline. They are inseparable concepts. This chapter will explain how to consciously start thinking about your future self—the one you are delaying gratification and suffering for. "

― Peter Hollins , The Science of Self-Discipline: The Willpower, Mental Toughness, and Self-Control to Resist Temptation and Achieve Your Goals