Katha Upanisad 1.3.3–4

Know the self as the rider, the body as the chariot, the intellect as the driver, and the mind as the reins.

आत्मानं रथिनं विद्धि शरीरं रथमेव च । बुद्धिं तु सारथिं विद्धि मनः प्रग्रहमेव च ॥

atmanam rathinam viddhi sariram ratham eva ca | buddhim tu sarathim viddhi manah pragraham eva ca ||

Know the self as the rider, the body as the chariot, the intellect as the driver, and the mind as the reins.

If the horses (senses and impulses) run, do not blame only the rider. Check sleep, food, company, and — when needed — a physician for the chariot itself.