Self-Confidence and the Birth of Vice

Duryodhana is not a fool and the epic never lets him be played as one. He is capable, courageous in the field, and entirely certain — and the certainty is what does the damage. He is warned by his father, by Bhishma, by Vidura, by Krishna in person, and each warning confirms him.

The Mahabharat's interest is in the hinge: the point at which self-belief stops taking in information. Karna's loyalty and Bhishma's vow are treated the same way, as strengths held past the point where they still served anything.