Kieran had so many questions for Scar that he asked individually, as expected. But a lot of the posed questions couldn't be answered. Apparently, they would spoil the meaning of the Trial of Inheritors.
It was designed explicitly to impart information, and Scar didn't wish to pervert or intrude upon the sanctity of the Trial of Inheritor's traditions.
Because of the Oath, however, rules were the more fitting term as opposed to traditions.
Still, Kieran was more knowledgeable now than he had been minutes before. As Agatha had said, the Vain did exist. They were those that "succeeded" but abandoned. However, Scar clued Kieran in on an integral piece of information.
Vains only encompassed part of the picture of failed Myths. It consisted of two halves, though the number difference between them was incomparably vast. The Vain was viewed as having a more tragic fate of the two.