Dumbledore oferece uma teoria no final de Ordem da Fênix : Voldemort baseou sua decisão na pureza do sangue, que é uma das únicas coisas que ele saberia sobre os dois garotos, e que ele pode comparar com o seu:
“But he might have chosen wrong!” said Harry. “He might have marked the wrong person!”
“He chose the boy he thought most likely to be a danger to him,” said Dumbledore. “And notice this, Harry. He chose, not the pureblood (which, according to his creed, is the only kind of wizard worth being or knowing), but the half-blood, like himself. He saw himself in you before he had ever seen you.”
— Order of the Phoenix, chapter 37 (The Lost Prophecy)
J.K. Rowling confirmou em uma entrevista que isso não era apenas uma teoria; esta foi a principal razão pela qual Voldemort foi atrás de Harry:
Why did Voldemort pick Harry and not Neville?
Dumbledore explains this in Order of the Phoenix. Voldemort identified more with the half-blood boy and therefore decided he must be the greater risk.
— J.K. Rowling World Book Day Chat (March 2004)