The ego rules the mind because it links the I with the mind and body. If the I, which is another name for the self, were not identified with the mind and body, the ego would have no power. Self-study [svadhyaya], therefore, is the set of practices that investigates the nature of the self to discover its origin. When the origin is found to be separate from the body, the ego loses the battle and peace is attain.

The Yoga Sutras of Patanjali, Book II, 2008