The weakest part of this novel is the attempt to show "humanity" through the underlying brother-sister relationship, because Card did not know how to deal with Valentine's character in relation to Ender's training. Chapter 13 is almost a different genre from the rest of the novel, and one Card is not comfortable with. The only viable sacrifice Ender makes by going to training school is the loss of constsnt contact with Valentine. The whole Demosthenes thread of the book doesn't ring true, and if Valentine's letter turned Ender away from his "ambition," it was only because Card did not know how to bring the novel back to human emotions and relationships. The underlying sense of the book--that we misunderstand our enemies--is sound, but the human deviations of emotions are only sketched out.