Self-Mastery Builds Your Self-Image
Every time you have self-mastery in any way, you build up your self-image. "I am a person who is gaining more and more control over my emotions and actions all the time." Every time you have the emotional self-control to do something that you find difficult to do, you build up your self-image. Every time you refrain from saying or doing something, you build up your self-image.
Some people keep self-mastery journals. Writing down their successes and victories in exhibiting self-control improves their ability to exhibit a greater amount of self-mastery.