Kṛṣṇa uses a nautical analogy to describe the vulnerability of the mind. Just as a strong wind sweeps away a boat on the water, even one of the roaming senses on which the mind focuses can carry away a person’s intelligence. You might have nine anchors down, but if one anchor is loose and the wind is strong, the boat will drift. If a person controls most of their habits but leaves one sense—like the tongue or the eyes—uncontrolled, that one hole will eventually sink the ship of their wisdom. The mind follows the sense that is most active. Therefore, total vigilance is required. Kṛṣṇa is telling Arjuna that he cannot afford to be ‘mostly’ disciplined; he must master all his senses so that his intelligence remains on course toward the spiritual goal.