10-Our army protected by Bhishma is unlimited (impossible to be counted), but that army of theirs, under protection of Bhima is limited.
11-However, all of you without exception taking charge of your divisions of the army, please protect Bhishma in particular.
12-The valiant grandfather of the Kurus, Bhishma, in order to raise Duryodhana’s spirit, blew his conch like a lion’s roar.
Duryodhan conceals the fear of Pandvas by saying that even if there are great maharathas in their army we outnumber them in counts. He believed that in war it is number that matters. He had shown his believe in the very beginning by accepting 11 akshauni sena in place of Lord Krishna. Duryodhan puts his belief in Bhishma with “अपर्याप्तं तदस्माकं बलं भीष्माभिरक्षितम् our army is unlimited protected by Bhisma” or rather power of our Army is unlimited protected by Bhisma. And then he counters his fear as well as informs Dron with “पर्याप्तं त्विदमेतेषां बलं भीमाभिरक्षितम् their army is limited (in power and number) under protection of Bhima“. He humiliates the teacher Dron by appreciating and putting faith in Bhisma in front of him who was no less a warrior. All these ignorance payed him litter.
In next verse Duryodha instructs Dron not just informs him, he says that special attention should be given to Bhisma (as he had faith in him) by all great maharathas. It seems from the above instruction that he even had no confidence in Bhishma. The verse twelve clears Duryodhan’s anxiety that deceptively conceal his fear. Bhisma knew this and blew his conch to ward of fear from Duryodhan’s heart.
Bhagwad Geeta 