Bhagavad Gita, Chapter 18, Verse 26

An agent who is free from attachment, non-egotistic, endued with fortitude and enthusiasm and unaffected in success or failure, is called Sâttvika.

Real steadiness through both success and failure is named here as what actually marks this kind of performer.

Enthusiasm and determination are paired with a real lack of ego, showing this isn't passive detachment, it's engaged effort without personal stake in the outcome. Real balance runs through both halves.