He does not obey the commands of his father who follows the path of virtue and worldly benefit. Duryodhana will bring on the destruction of the Kurus by his acts.
अतिक्रामति यः शास्त्रं पितुर्धर्मार्थदर्शिनः। एते नश्यन्ति कुरवो दुर्योधनकृतेन वै॥