In Book 4 of Jalaluddin Rumi's Masnavi, the tale of the tanner's brother serves as a striking allegory for spiritual habituation and the corrupting influence of worldly desires. In the story, a man accustomed to the foul stench of a tannery collapses when exposed to the sweet fragrances of the perfume market. While bystanders unsuccessfully try to revive him with rosewater and musk, his brother cures him by secretly holding dog's dung to his nose. Rumi uses this narrative to illustrate how individuals entrenched in corruption and sin become spiritually repelled by divine truth and moral counsel. Just as a worm born in dung cannot tolerate ambergris, a soul habituated to impurity cannot endure the 'musk' of spiritual wisdom. Rumi warns that without a transformative shower of divine light, such an individual remains trapped in their base nature, rejecting the very spiritual remedies that could save them.