Chapter 6 · verse 36 · gita.yoga.org

Bhagavad Gita 6.36

असंयतात्मना योगो दुष्प्राप इति मे मतिः। वश्यात्मना तु यतता शक्योऽवाप्तुमुपायतः

I think Yoga is hard to be attained by one with an uncontrolled self, but the self-controlled and striving one can attain it by the appropriate means.