Long back before the Mahabharata war, Pandavas were living in exile in a forest. Duryodhana placed his camp on the opposite side of the pond where Pandavas were staying. Once while Duryodhana was taking bath in that pond, the heavenly prince Gandharvas came to take bath Duryodhana could not tolerate this and had a fight in which Gandharva captured him. On request of Yudhisthir, Arjuna saved Duryodhana and set him free. Duryodhana was ashamed but being a kshatriya, asked Arjuna what benediction of boon would he like Arjuna replied he would ask for the honour gift later when he needed it. It was during that night of Mahabharata war, when Krishna reminded Arjuna of his unsatisfied boon and told him to go to Duryodhana and ask for 5 golden arrows. When Arjuna asked for the arrows Duryodhana was shocked being a kshatriya and bound by his promise he had to give those golden arrows. He asked who told you about golden arrows, Arjuna replied who else other than Lord Krishna.
Duryodhana again went to Bhisma and requested for another five golden arrows. To this Bhisma laughed and replied this is not possible and will of Lord is Supreme and undeniable and whatever happens tomorrow in the Mahabharat war is written long before.