To illustrate exactly *why* an undisciplined mind fails to achieve peace (as stated in Verse 66), Krishna provides a terrifying and beautiful metaphor. He says that among the roaming senses (indriyāṇāṃ hi caratāṃ), if the mind yields to and follows even *one* of them (yan mano 'nuvidhīyate), that single sense will sweep away the person's entire intellect and wisdom (tad asya harati prajñāṃ). He compares it to a gale-force wind (vāyur) sweeping a boat (nāvam) off its course on the water (ambhasi).