You shouldn't do something just because someone asks you.
James is a Marine, and his Sergeant wanted him to shoot a prisoner they had.
James has to respond to his Sergeant.
James tells his Sergeant that he won't do it since it'd be against the law.
James takes out his gun and aims it right at the prisoner's head.
James doesn't have to kill anyone even though the Sergeant becomes mad.
James commits a war crime, and his Sergeant feels that he can get James to do anything.