Harry Potter has had loads of experience with not being believed. Let's take a tour through the first four books, shall we?
Harry gets through all of this doubt and mistrust from the people around him by leaning on his best friends, Ron and Hermione. They (mostly) stand by him through thick and thin. After a lonely, friendless childhood in the Muggle world, Harry is incredibly relieved to have friends; their support helps him through some very tough times.
That is, in Books 1 through 4. By Book 5, the troubles Harry has to deal with have gotten huge: he saw Voldemort return to life with his own two eyes at the end of Book 4. But the Ministry of Magic is in so much denial that they use the Daily Prophet to discredit him. Most of the wizarding world now thinks Harry is nuts, that he’s an attention-seeking kid with paranoid delusions. To make matters worse, Hogwarts has been saddled with a new Defense Against the Dark Arts teacher straight from the Ministry, Dolores Umbridge. She uses her position of authority to target Harry personally, insisting that Harry is lying about Voldemort. To top off all of this stress, Harry also has to prepare for his Ordinary Wizarding Levels – exams set for all Hogwarts students at the end of their fifth year to evaluate their school progress so far. And he's having lady troubles with his long-time crush, Cho Chang.
Harry spends most of Book 5 in so much pain that he lashes out even at those close friends that have stood by him in Books 1 through 4. Harry shouts at Ron and Hermione so often that Ginny, Fred, and George all comment on his behavior. Fred, for example, laughs, "You don't want to bottle up your anger like that, Harry, let it all out [...]. There might be a couple of people fifty miles away who didn't hear you" (4.105).
Harry's rage can make Book 5 a little tough to read at times, because one of our favorite things about the first four books is Harry's caring relationship with Ron and Hermione. Sure, their friendships aren't perfect: Ron goes through a long bout of jealousy of Harry in Book 4, and Ron and Hermione have a falling out over Crookshanks the cat and the disappearance of Ron's rat, Scabbers, in Book 3. But Harry has never been isolated from both of his dearest friends at the same time before, and it makes him cranky, grumpy, and all around difficult to take. Sometimes you just want to shake the guy and tell him to snap out of it.
Rowling has acknowledged that Harry is kind of obnoxious in Book 5. But she has also promised that this extended wrath he feels is absolutely necessary to the character's development. Harry's gone through a lot in the previous four years, and it's all catching up to him right now. Why should Harry have to be the one to see all of these horrible things and then be punished for it by Professor Umbridge and the Ministry? It's not fair, and Harry has a right to be mad (even if it makes him less fun to read). She comments:
Well, Phoenix, I would say, in self-defense – Harry had to, because of what I'm trying to say about Harry as a hero. Because he's a very human hero, and this is, obviously, there's a contrast, between him, as a very human hero, and Voldemort, who has deliberately dehumanized himself. [...] And Harry, therefore, did have to reach a point where he did almost break down, and say he didn't want to play anymore, he didn't want to be the hero anymore – and he'd lost too much. And he didn't want to lose anything else. So that – Phoenix was the point at which I decided he would have his breakdown. (source)
What do you think: is all of Harry's frustration necessary for his character development? Does it make him seem more realistic?
Harry spends Book 5 being kind of a jerk, but if anybody has earned the right to lash out in this series, it's Harry. So we keep reading, even when he's being self-destructive and hard to like. The thing is, Harry is always full of feeling – even when it's negative feeling – which is what makes him sympathetic and relatable to his audience. His arch-nemesis Voldemort could never feel as strongly as Harry does. Perhaps it's Harry's feelings, which are so all-encompassing and important in Book 5, that give Harry the prophesied "power the Dark Lord knows not" (37.191)? And these feelings are also what make him, in J.K. Rowling's words, "a very human hero."
(Obviously, no analysis of Harry in Book 5 would be complete without talking about his relationships to Voldemort, Professor Dumbledore, and Cho Chang – check out our thoughts on these characters for more on Harry's anger, resentment, and developing hormones.)