In Section 27 of Book Five, Rumi explores the detrimental effects of excessive analytical thought (فکرت) on the spiritual purity of the tranquil soul (نفس مطمئن��). He employs the metaphor of a poisonous nail scratching the surface of the soul to illustrate how discursive thinking leaves a lasting blemish. Just as engraving on a clear mirror leaves a permanent mark or defect even after it is wiped, overthinking perturbs the simplicity and clarity required for true spiritual insight, emphasizing the limitations of human rationality.