Know that the Self is the rider, and the body the chariot; that the intellect is the charioteer, and the mind the reins.
The senses, say the wise, are the horses; the roads they travel are the mazes of desire….
When a man lacks discrimination and his mind is uncontrolled, his senses are unmanageable, like the restive horses of a charioteer.
But when a man has discrimination and his mind is controlled, his senses, like the well-broken horses of a charioteer, lightly obey the rein.
Katha Upanishad 1.3.3-6