“The mind is difficult to control, swift, and prone to wander wherever it wishes. But a disciplined and well-governed mind brings true happiness.”
Canonical Pali Original: Dunniggahassa lahuno, yatthakāmanipātino; Cittassa damatho sādhu, cittaṃ dantaṃ sukhāvahaṃ.
— Gautam Buddha
The Awakened One, Founder of Dhamma
Pali Canon: Dhammapada 3.35 on the mental discipline and mindful training of consciousness.