Jonathon's flaw is that he can't differentiate between which events are par for adolescence and which are signs of something genuinely wrong. Kimball uses this to great effect, allowing the combination of Jonathon's richly drawn disorders and his self-destructing family to cast doubt on the psychological cause and effect.
As the letters pile up, Jonathon's voice is tempered by his brother's commentary, which comes through in occasional footnotes and in interviews with their father. Robert is initially skeptical of Jonathon's recollections -- right away he says that "Jonathon's version may have been true for him, but I was the favorite and I don't remember it like that." In one of the book's rare missteps, the truth behind the worst of these indictments is never fully revealed, leaving both Robert and the reader lost as to the severity of the father's crimes.
