Sri-bhagavan uvaca
bandhur atmatmanas tasya
yenatmaivatmana jitah
anatmanas tu satrutve
vartetatmaiva satru-vat
yenatmaivatmana jitah
anatmanas tu satrutve
vartetatmaiva satru-vat
Meaning: For him who has conquered the mind, the mind is the best friends; but for one who has failed to do so, his mind will remain the greatest enemy.
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One who cannot control his mind lives always with the greatest enemy, and thus his life and its mission are spoiled
Bhagavad Gita: For him who has conquered the mind, the mind is the best of friends (Dhyana-yoga (Text 06, Ch 6))