बुद्धियुक्तो जहातीह उभे सुकृतदुष्कृते।तस्माद्योगाय युज्यस्व योगः कर्मसु कौशलम्॥
buddhi-yukto jahātīha ubhe sukṛta-duṣkṛtetasmād yogāya yujyasva yogaḥ karmasu kauśalam
Word by word
The verse says
A person joined to that mind sheds both the good he has done and the bad, right here in this life. So give yourself to yoga. Yoga is doing a thing well.
In plain words
Two remarkable claims in one verse.
First: you drop both good and bad deeds. Not just the bad. Both.
Then the definition everybody quotes: yogaḥ karmasu kauśalam - yoga is skill in action.
Where you've felt this · in sport
Watch a good mason lay brick. Nothing is wasted, nothing is forced, and he is not thinking about being watched. That is not the absence of effort. It is effort with nothing extra left in it.
Going deeper
Start with the strange half. Why would you want to shed good deeds?
Because in this framework merit binds exactly as demerit does. Good karma buys a pleasant result, and a result is a place you have to go and collect. Both ledgers keep you in the system. What Krishna is describing is not becoming very good at accumulating credit; it is stepping out of the accounting.
Iha - right here, in this life. Not after death. The release is presented as available now.
Then the famous line, which is routinely mistranslated into a motivational slogan. Yogaḥ karmasu kauśalam is not work hard and call it spiritual practice.
Kauśalam is skill, deftness, the quality of doing a thing without waste. In context it means the skill of acting in the way just described - doing the work fully while attached to none of it. That is the skill being named.
So the verse is not saying yoga is excellence at your job. It is saying that acting without grabbing at the fruit is itself a skill, and one you can get better at.