Why does Hazel want to track down the author of An Imperial Affliction?

An Imperial Affliction is Hazel's favorite book. She completely identifies with the central character, Anna, who, like Hazel, is a young adult with terminal cancer. She tells Augustus it's the only book she's read that matches her own experiences of living with the disease.
Although Hazel loves the book, she's unsatisfied by its ambiguous ending, which ends mid-sentence. She's understandably curious as to why this is and also why the elusive author of An Imperial Affliction, Peter Van Houten, fled to Amsterdam after the book was published. Only Peter himself can answer these questions, so it's perfectly natural for Hazel to want to track him down.
Amazingly, Augustus reveals that he's been in touch with Peter, carrying on an email correspondence through his assistant. Eventually, Hazel and Augustus travel to Amsterdam to ask Peter their questions in person. Unfortunately, they are disappointed by the author's behavior, as he comes across as a rude, mean-spirited drunk.