मुक्तसङ्गोऽनहंवादी धृत्युत्साहसमन्वितः। सिद्ध्यसिद्ध्योर्निर्विकारः कर्ता सात्त्विक उच्यते ॥

mukta-saṅgo ‘nahaṁ-vādī dhṛity-utsāha-samanvitaḥ siddhy-asiddhyor nirvikāraḥ kartā sāttvika uchyate

Liberated from attachment, not egoistic, endued with firmness and confidence, unchanged by success or failure, that actor is called pure.

In plain words: A pure doer is free from clinging and ego. They are steady and full of energy, and they stay the same whether they succeed or fail.