
Arjuna expresses doubt about the practicality of yoga. 'Yo 'yaṁ yogas tvayā proktaḥ sāmyena'—this (ayam) yoga (yogaḥ) that you (tvayā) have described (proktaḥ) by equanimity (sāmyena). This means: Arjuna is referring to the yoga of equanimity, the balanced state, that Krishna has been describing. 'Etasya ahaṁ na paśyāmi cañcalatvāt sthitim sthirām'—I (aham) do not see (na paśyāmi) how firm (sthirām) stability (sthitim) of this (etasya) can be maintained, because of (tvāt) restlessness (cañcalatvāt). This means: Arjuna is honest about his doubt—he doesn't see how this yoga can be maintained because the mind is restless. The mind is fickle, unstable, constantly moving—how can one maintain equanimity? This is a sincere question from someone who's trying to practice but finding it difficult. Arjuna isn't rejecting the teaching—he's expressing the practical challenge he faces.
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