Yudhishthira said He never thought anybody his equal in wisdom. It is for that sin that prince has dropped down.
युधिष्ठिर उवाच आत्मनः सदृशं प्राज्ञं नैषोऽमन्यत कंचन। तेन दोषेण पतितस्तस्मादेव नृपात्मजः॥