Lord Krishna reasons with a confused Arjuna, reminding him of his duties, and uses many arguments to make Arjuna see reason, said Valayapet Ramachariar, in a discourse. He tells him that if he does not fight, then Duryodhana and Karna will mock him.
An example of a similar reason being given for the need to fight, is seen in the Ramayana. Sugriva challenges Vali to a fight. Tara, the wife of Vali, knows that because Rama supports Sugriva, her husband Vali is definitely going to lose the fight. So Tara tells Vali not to fight. Vali tells her that he has faith in Rama’s adherence to dharma. If because of Rama’s adherence to dharma, Vali were to die, then he will welcome such a death. If Vali does not go when Sugriva calls him out to fight, none of the monkeys will say that it is because of Rama that Vali refused to fight. They will say it is fear of Sugriva that kept Vali from fighting. So in order to safeguard his reputation, Vali goes out to fight. The first time Sugriva is soundly thrashed by Vali, and it is only later that Rama kills Vali. So we remember Sugriva as the one who was first beaten up by Vali. But if Vali had refused to fight, then we would remember Vali as the coward who refused to fight Sugriva!
In the same way if Arjuna refuses to fight, even an ordinary foot soldier in the Kaurava army will boast that it is because of his own prowess that Arjuna backed out of the fight! A maternal uncle has a respected position in a person’s life, and is the first to bless a child. But Krishna’s maternal uncle Kamsa had been cruel, and so Krishna had killed him. So Arjuna should not cite relationship as an excuse for refusing to fight Bhishma, points out Krishna.