Bhagavad Gita, Chapter 3, Verse 22

I have, O son of Prithâ, no duty in the three worlds, nothing I have not already gained, and nothing left to gain; yet I continue in action.

Even with nothing personal left to gain, showing up and doing the work still matters.

Krishna has no unmet need pushing him toward action, and acts anyway, purely for the sake of others. That's offered here as the clearest possible model: real duty doesn't require a personal payoff to be worth doing.