Bhagavad Gita, Chapter 12, Verse 15

He by whom the world is not agitated and who cannot be agitated by the world, who is freed from joy, envy, fear and anxiety, he is dear to Me.

Steady in both directions: not disturbing the world, and not easily thrown by it.

Equanimity here works both ways, neither upsetting others nor being upset by them. That symmetry is what marks the quality as complete rather than one-sided.