That truth-abiding one (Bhishma) himself ordained his own death in battle. And your respectable self too does not exert your best because Arjuna is your disciple.
स्वयं हि मृत्युर्विहितः सत्यसंधेन संयुगे। भवानुपेक्षां कुरुते शिष्यत्वादर्जुनस्य हि॥