Bhagavad Gita
Chapter 6 · Verse 5
उद्धरेदात्मनात्मानं नात्मानमवसादयेत्। आत्मैव ह्यात्मनो बन्धुरात्मैव रिपुरात्मनः॥
uddhared ātmanātmānaṁ nātmānam avasādayet, ātmaiva hy ātmano bandhur ātmaiva ripur ātmanaḥ
You carry both your greatest support and your biggest obstacle in the same place: how you direct your own mind.
Lift yourself by your own mind. It can be your closest friend or your fiercest enemy.