This is the second rule for the Mastery of Desire by Theron Q. Dumont from his work titled, The Master Mind. Links to the first rule as well as a site to read the book for free on will be posted at the bottom of the page.
Refuse to permit the formation of the habit of expression in action the feeling, or emotion, or the desire arising therefrom, which are deemed objectionable. This second rule ties in closely to the first which is: Refrain so far as is possible from indulging in the physical expression of a feeling, emotion, or desire which you wish to conquer, control, and repress.
In a nutshell, once you express a feeling, emotion, or desire in action more then once you begin to form a habit. Habits create pathways in the mind which eases the travel of those feelings, emotions, and desires which you express. Therefore, once you repeatedly express anger physically it will become easier and easier for that emotion to flow through you mind because you have created a deep channel in the mind for its travel. The emotion will then expand and strengthen to fill the channel as you deepen it through repeated expression.
Form the habit of expressing in action the feeling, emotion, or desire which you wish to cultivate, develop, and strengthen.
This is the positive pole of the second rule of the Mastery of Desire. Every time you express a mental state, the easier it becomes to express it again. If you wish to cultivate the feeling of happiness or joy then the formation of this habit can be as simple as smiling more often, or by replacing bad thoughts with good ones and by choosing to view life from a positive perspective whenever you catch yourself looking at life through a negative perspective.
If you wish to feel more courageous, then form the habit of expressing courage physically. Stand up straight with your shoulders back. Look straight ahead and most importantly, act courageously. Say what you have to say. Stand up for yourself and soon the habit will be formed and the channel deepened and it will be much easier for you to be courageous.
Perhaps the most important concept to keep in mind is that all things take time and practice, and by persevering one can accomplish anything that one sets out to do.