Bhagavad Gita
Bhagavad Gita on Discipline and Practice
Discipline here is closer to yoga and abhyāsa than to harsh self-punishment. The Gita insists the mind is difficult, and still trainable.
These verses assume a path of practice. They are not a productivity hack.
Bhagavad Gita 6.5
One should lift the self by the self and not degrade the self.
Man should uplift himself by his own self and not degrade himself; for the Self alone is the friend of the Self, and the Self alone is the enemy of the Self.
Bhagavad Gita 6.6
The self is a friend or enemy according to whether it has been mastered.
For him who has conquered the lower self (senses, etc.) by the higher Self, the Self is his friend; but for him who has not conquered the senses, the Self remains like an enemy.
Bhagavad Gita 6.26
Wherever the restless mind wanders, it should be brought back under control.
Whatever causes this restless and unsteady mind to wander—by restraining those, the aspirant should bring it under the control of the Self alone.
Bhagavad Gita 6.35
The mind is restless, but is restrained by practice and dispassion.
Shri Bhagavan said: O mighty-armed one! Without doubt the mind is restless and difficult to control; but, O son of Kunti! it can be subdued by practice and dispassion.