Bhagavad Gita 6.5
उद्धरेदात्मनात्मानं नात्मानमवसादयेत्। आत्मैव ह्यात्मनो बन्धुरात्मैव रिपुरात्मनः॥
Easy meaning
Lift yourself up with your own good thoughts — don’t put yourself down. Your mind can be your best friend, or your hardest critic.
When to use
When a child says “I can’t” or feels small after a mistake.