Loss of enthusiasm, futile effort, fatigue, and mental agitation: this quartet of difficulties afflicts the yogīs.

The kaṣṭa-catuṣṭaya — the quartet of difficulties — is a clinical diagnosis of the practitioner. Utsāha-bhraṃśa: the collapse of initial impetus, when novelty fades and practice becomes a dull routine. Āyāsa: effort that bears no fruit, mechanical repetition without attention. Klānti: the physical and mental exhaustion that results from forcing. Mano-dhṛti: the agitation that occurs when the mind, weary of being controlled, rebels. These four form a pathological sequence: the loss of enthusiasm leads to strained effort, which produces fatigue, which culminates in mental rebellion. Patañjali anticipates this in Yoga Sūtra I.30: styāna — lethargy — as an obstacle. Vasiṣṭha expands on this: it is not merely lethargy but the entire cycle of motivational collapse. The solution is not more discipline, but kauśalam — skill, intelligence in effort. The Gītā II.50 defines yoga as karma-kauśalam: skill in action. Not more force, but better technique.