If a king wishes to capture a city of the enemy, he first takes control of the water supply and the supply of food: thus the enemy submits to him, reduced by famine.  So it is with the passions of the flesh too: if a person exists with fasting and hunger, the enemy wastes away from his soul.

—Abba John Colobos
Give Me a Word: The Alphabetical Sayings of the Desert Fathers