Bhagavad Gita Chapter 6, Verse 36

असंयतात्मना योगो दुष्प्राप इति मे मतिः | वश्यात्मना तु यतता शक्योऽवाप्तुमुपायतः ||

asaṁyatātmanā yogo duṣprāpa iti me matiḥ vaśyātmanā tu yatatā śakyo 'vāptum upāyataḥ

Yoga is difficult to attain for one whose mind is unbridled. But for one who has mastered the mind and strives earnestly, it is possible to attain by proper means.

Krishna explains the difference between the unbridled and mastered mind. 'Asaṁyatātmanā yogo duṣprāpa iti me matiḥ'—yoga (yogaḥ) is difficult to attain (duṣprāpaḥ) for one whose mind (ātmanā) is uncontrolled (asaṁyata), this is my (me) understanding (matiḥ). This means: when your mind is unbridled—uncontrolled, unrestrained, wild—yoga is very difficult to attain. You can't achieve union, peace, or realization when your mind is running wild. 'Vaśyātmanā tu yatatā śakyo 'vāptum upāyataḥ'—but (tu), for one who has mastered (vaśya) the mind (ātmanā) and strives (yatatā), it is possible (śakyaḥ) to attain (avāptum) by proper means (upāyataḥ). This means: when your mind is controlled—mastered, disciplined, restrained—and you strive earnestly, yoga becomes possible. You can attain it through proper means—through practice, detachment, the methods described. This is the contrast: unbridled mind makes yoga difficult, mastered mind makes it possible. The key is mastering the mind first, then striving earnestly.