Will power is the keynote of mastery, and asceticism is the development of will power.
Commentary by Hazrat Inayat Khan:
The first exercise to help the will power to develop would be to check every act, word, and thought which we do not wish to occur; to avoid unintentional actions, speech, and thoughts. The other exercise that is necessary for the development of the will power is that of seeing that neither our mind nor our body rules us, but that we rule our body and our mind. Desires such as appetite, thirst, sleep, even the desire of moving or standing or walking, all these desires should be under control. There should be a time in every day when every desire of the body is checked. See if you can do it; and then as long as you can let the body go without listening to it, do so.