Know the Self as Lord of the chariot, the body as the chariot itself, the discriminating intellect as the charioteer, and the mind as the reins. The senses, say the wise are the horses. Selfish desires are the roads they travel, Katha Upanishad
The Upanishads say that your body is like a chariot drawn by five powerful horses, the five senses. These horses travel not so much through space as through time. They gallop from birth towards death, pursuing the objects of their desire. The discriminating intellect as the charioteer, whose job it is to not to drive you over a cliff. The reins he holds are the mind–your thoughts, emotions and desires.
The image is packed with implications. For one, the job of the intellect is to see clearly. The job of the mind is to act as the reins. When everything is working in harmony our highest Self makes all the decisions. The intellect conveys these decisions to the mind, and the senses obey the mind.
But when the senses are uncontrolled, they immediately take the road they like best: personal satisfactions, mostly pleasure. Then we are not making the decisions: the horses are.