At first glance, Peter Van Houten doesn't seem like the greatest mentor. After all, who wants an adult role model who drinks like a fish and says totally offensive things to kids with cancer? But all of that stuff, as off-putting as it is, doesn't matter. Why? Because Peter Van Houten's book has a profound effect on Hazel Grace and Augustus. It guides them as they navigate their adolescence and their illnesses. In the end, Hazel Grace speaks to Van Houten at Augustus's funeral and learns that he knows what they are going through because his daughter died of cancer, too. He teaches them how to deal with their illness by showing them how not to let it rule their lives and destroy them.