From sattva-guṇa is born knowledge, wisdom. From rajas arises greed. Inattention and delusion, coupled with ignorance, result from tamas.
Krishna is describing the effect of each guna briefly. To whatever he has stated already, Krishna adds that sattva alone instils knowledge.
Rajas stirs up all kinds of desires and emotional preferences. Greed is a common trait rajas produces. It dominates almost all. On getting intensified, it can lead to any extent of assault and vehemence.
Tamas envelops one’s mind and intelligence with ignorance, delusion. The plight makes the victim refuse to listen to any comment or advice. He believes and insists that he alone is correct. He is averse to any kind of input from anyone. Tāmasa delusion is too hard to drop or overcome. Imagine the plight under the spell of gunas! But sattva, however, has a loving hand of relief and hope for the earnest seekers!