Chapter III Sloka 28

tvivu mhabahae gu[kmRiv-agyae>, 
gu[a gu[e;u vtRNt #it mTva n ste.

tattvavittu mahbho 
guakarmavibhgayo | 
gu gueu vartanta 
iti matv na sajjate ( 3|28)||

But he who knows the truth, O mighty-armed (Arjuna),
about the roles of the Gunas and (their) functions,
and who knows that Gunas-as-the-senses
move amidst Gunas-as-objects,
- he is not attached.

Tattvavit = One who knows the Reality, the Self.

In all activities, it is the mind that projects out to form action. Understanding this, the wise man realises that action belongs to the world of mind and his no more anxious for the fruits thereof. Success and failure belong to the mind, and not to him.