Krishna is contrasting two kinds of workers: one who acts and releases, one who acts and clings. This verse is a compressed summary of the yoga of action, showing what steadiness looks like in practice versus what craving looks like.
yuktaḥ karmaphalaṃ tyaktvā śāntim āpnoti naiṣṭhikīm | ayuktaḥ kāmakāreṇa phale sakto nibadhyate ||
The disciplined person, giving up the fruit of action, attains abiding peace. The undisciplined person, driven by desire and attached to the result, becomes bound.
Krishna is not saying the yuktaḥ is a good person and the ayuktaḥ is a bad one. He is describing two mechanical states. One produces binding, one produces freedom. The description is as neutral as saying water flows downhill. The bound person is not blamed; their state is simply shown.
The sharpest thing in this verse is kāmakāreṇa: desire doing the doing. There is a recognizable difference between acting from a clear decision and being pulled by wanting. In the second case, the thinking that precedes action is not really thinking. It is rationalization. The wanting already decided; the mind is just building a case.
Naiṣṭhikīm śānti (the settled peace) arrives because the mechanism that was generating noise has been switched off. When you are not running your actions on the fuel of needed outcomes, the anxious monitoring that normally accompanies action simply stops. The quiet is not earned. It is what is left when the noise-maker is gone.
Nibadhyate is present tense: the person is being bound, continuously. Each desire-driven action tightens the bind a little more. This is important because it means the cost is not just in the moment of a bad outcome. The binding happens through the habit itself, regardless of whether the outcome is good or bad.
Person A ships a product feature, but for weeks before launch they're checking metrics obsessively, rehearsing what they'll say if it flops, quietly making it mean something about their worth. The outcome lands, good or bad, and they are either briefly relieved or deflated. Then the cycle starts again with the next thing. Person B builds the same feature with the same care. They want it to succeed. But they finish it and release it the way you'd release a letter into a mailbox. After that it belongs to the world. They check the metrics once, note what's useful, and are already thinking about the next problem. Their baseline doesn't rise and fall with the numbers.
Verse 5.13 moves inward: having shown what freedom from fruit-attachment produces, Krishna now describes the one who has truly renounced acting through the nine-gated city of the body, neither acting nor causing action. When ready, say: "5.13"