तत्र सत्त्वं निर्मलत्वात्प्रकाशकमनामयम्।सुखसङ्गेन बध्नाति ज्ञानसङ्गेन चानघ॥
tatra sattvaṃ nirmalatvāt prakāśakam anāmayamsukha-saṅgena badhnāti jñāna-saṅgena cānagha
Word by word
The verse says
Of these, clarity is pure and lights things up, and it is free of trouble. It binds by attachment to pleasure, Arjuna, and by attachment to knowing.
In plain words
The good one binds in two ways, and both are easy to miss.
By pleasure — the mild, clean pleasure of things going well.
And by jñāna-saṅga — attachment to knowing. The grip of being somebody who understands.
Where you've felt this · in study
Your colleague has read everything there is on his subject. He finds it oddly hard to say I do not know. It is not vanity. Understanding has become part of how he is at ease in a room, and the not-knowing costs him something that has nothing to do with the question.
Going deeper
Attachment to knowledge is the subtlest binding in the book and it is named here in two words.
The cruder attachments are easy to spot in yourself. Wanting money, wanting to win, wanting to be left alone. Jñāna-saṅga is harder, because the thing being gripped is good and the gripping looks like diligence. A person can be genuinely clear-sighted and entirely held by being so.
This is also the honest reason the chapter will not let clarity be the goal.
There is a specific form of this that affects anybody reading a book like this one. Understanding the three strands, being able to name them, noticing them in other people — all of that is clarity, and all of it is available to be gripped. The verse names that before you have finished the chapter, which is a kindness of a sort.