नियतस्य तु संन्यासः कर्मणो नोपपद्यते।मोहात्तस्य परित्यागस्तामसः परिकीर्तितः॥
niyatasya tu sannyāsaḥ karmaṇo nopapadyatemohāt tasya parityāgas tāmasaḥ parikīrtitaḥ
Word by word
The verse says
Giving up work that is genuinely yours to do is not right. To abandon it out of confusion is called dark renunciation.
In plain words
Here is the first of the three kinds, and it is the worst one.
Walking away from work that was actually yours. Not because you worked out that you should, but because you were confused and it felt like a way out.
That is called tāmasa - the heavy, dull kind. And notice it is still called renunciation. From outside it looks exactly like the real thing.
Where you've felt this · at work
Your cousin stops going to his classes in the second year. He tells everyone he has realised the degree is pointless. He has not realised anything. He fell behind in one subject in October, could not face asking for help, and the story about pointlessness arrived afterwards to make the not-going bearable.
Going deeper
A retreat that arrives with a philosophy attached is the thing being described, and the philosophy is nearly always written after the retreat.
The word used is confusion, not cowardice, and that is deliberate. The person is not lying. By the time they explain themselves they genuinely believe the explanation. What they cannot see is the order in which it happened: first the flinch, then the reason.
This is also the most important verse in the chapter for Arjuna personally. He opened the book by putting down his bow and giving excellent reasons. Krishna is telling him, late and quietly, which category that belonged to.
The test is the sequence. Did you decide, and then stop? Or did you stop, and then find the words? Most people can remember honestly which way round it went, if they ask within a day or two.