Chapter 6 · The Yoga of Meditation · Krishna said
Bhagavad Gita 6.36 — Yoga by right effort
असंयतात्मना योगो दुष्प्राप इति मे मतिः। वश्यात्मना तु यतता शक्योऽवाप्तुमुपायतः ॥
asaṃyatātmanā yogo duṣprāpa iti me matiḥ | vaśyātmanā tu yatatā śakyo'vāptumupāyataḥ ||
Meaning
In my view, yoga is hard to reach for one whose mind is uncontrolled. But one who controls the mind and strives by the right means can attain it.