asamyatatmana yogo
dusprapa iti me matih
vasyatmana tu yatata
sakyo vaptum upayatah
(Dhyana-yoga, Text 36 Chapter 6)
Meaning:
For one whose mind is unbridled, self realization is difficult work. But he whose mind is controlled and who strives by appropriate means is assured of success. That is My opinion.
Bhagavad Gita: Assured of success (Dhyana-Yoga, Text 36 Chapter 6)