Āsana becomes perfect when all effort or strain, prayatna, ceases and the body no longer trembles, says Vyāsa, and when the citta is absorbed in the infinite, ananta.
This passage articulates the paradox central to yogic psychology: the telos of disciplined effort is its own self-cancellation in absorbed, effortless stillness.
, The Yoga Sutras of Patanjali: A New Edition, Translation, and Commentary, 2009thesis