For one who has conquered the self by the self, the self is a friend. But for one who has not conquered the self, the self acts as an enemy.

Direct continuation of the previous verse, clarifying the condition:

Yena ātmā eva ātmanā jitaḥ — for one whose self has been conquered by the self itself. Jita means conquered, mastered, pacified.

What is “conquering the self”? It’s when conscious will dominates automatic impulses, when the higher aspects of the mind govern the lower ones.

Bandhur ātmā ātmanaḥ — then the self is friend of the self. The mind becomes an ally: it cooperates, supports, sustains.

Anātmanaḥ tu śatrutve vartetā ātmā eva śatruvat — but for the unconquered, the self acts as an enemy.

Anātmanaḥ — literally “without self,” but here means one who has not integrated their self, who is internally divided.

The unconquered mind sabotages: it procrastinates, distracts, justifies, fears, desires what harms. It acts literally śatruvat — like an enemy.

Yoga is precisely this inner conquest.