Bhagavad Gita Chapter 2, Verse 67

इन्द्रियाणां हि चरतां यन्मनोऽनुविधीयते । तदस्य हरति प्रज्ञां वायुर्नावमिवाम्भसि ॥

indriyāṇāṁ hi caratāṁ yan mano 'nuvidhīyate | tad asya harati prajñāṁ vāyur nāvam ivāmbhasi ||

Indeed, when the mind follows the wandering senses, that carries away one's wisdom, like wind carries a boat on water.

Krishna reveals the mechanism from verse 2.66—how wisdom gets lost. Your senses naturally roam (indriyāṇāṁ caratām)—eyes scanning, ears seeking. The problem isn't this; it's when your mind becomes subordinate (mano 'nuvidhīyate) and follows them helplessly. This should be reversed: mind directs senses. But when mind follows instead, wisdom gets stolen (harati prajñām)—like wind blowing a boat on water (vāyur nāvam iva). A boat needs a helmsman steering; here it's blown helplessly. Similarly, your prajñā (discriminative wisdom) gets carried away when mind chases every sense impression.