यया धर्ममधर्मं च कार्यं चाकार्यमेव च। अयथावत्प्रजानाति बुद्धिः सा पार्थ राजसी ॥

yayā dharmam adharmaṁ cha kāryaṁ chākāryam eva cha ayathāvat prajānāti buddhiḥ sā pārtha rājasī

That by which one understandeth away Right and Wrong and also what ought to be done and what ought not to be done, that Reason, O Pârtha, is passionate.

In plain words: Understanding ruled by passion is confused about right and wrong. It cannot clearly tell what should be done and what should not.