That resolve by which a dull-witted person does not let go of sleep, fear, grief, despair, and also arrogance, O son of Pritha, is tamasic.
Explanation
Krishna is describing three kinds of steadfastness or resolve (dhṛti), matching the three qualities (guṇa) of nature. Here he names the lowest, tamasic (tāmasī), the quality of dullness and inertia. It is a stubborn clinging to sleep, fear, grief, despair and conceit, and a refusal to move beyond them. Some readers take this as plain persistence in bad habits, others as a mind too clouded to rise above them.