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In a lot of ways, Hermione is the anti-Harry in this book. She's mature, thoughtful, and perceptive. And, as always, she's darned smart. When Harry gets out of line, Hermione is there to remind Harry that she and Ron believe in him, so he should stop taking out his anger on his best friends. Whenever Harry wants to rush in blindly, to act, Hermione is always the one who advises him to be cautious. This proves most important when Harry wants to go to the Department of Mysteries to find Sirius. It's Hermione who asks the important questions. Could those "visions" you're seeing actually be dreams? Are you sure that Sirius is truly in danger? Couldn't this be a trap set by Voldemort? And Hermione turns out to be right.
Still, even though Hermione is much more careful than Harry, four-plus years of exposure to Ron and Harry have encouraged in her a sense of daring. When Harry and Hermione get caught by Professor Umbridge trying to get in touch with Number Twelve, Grimmauld Place, Hermione is the one who comes up with the idea on the spot to lure Professor Umbridge into the Forbidden Forest where the centaurs trample her. Even, when Hermione thinks Harry is being foolish, she is still always willing to help him out of a jam. She accompanies Harry to the Department of Mysteries despite her uncertainty that Sirius is being tortured there.
What's more, it is Hermione who has such faith in Harry's skills as a Defense Against the Dark Arts teacher that she suggests they start a secret defense club against Professor Umbridge's rules and right under her nose. As Harry gets involved in teaching defense to those who want to learn, his confidence rises in leaps and bounds, and it's all thanks to Hermione. She sets up the initial meeting of the Defense Association/Dumbledore's Army. She figures out a method to keep all of the members in touch (enchanted gold coins). And she jinxes the list of names so that, when Marietta Edgecombe rats out the D.A. to Professor Umbridge, she is left with a horrible facial disfiguration that reads, "SNEAK" (27.146) in red pustules. Hermione's magic is so strong that Professor Umbridge can't figure out how to undo the curse on this traitor.
So, to sum up, Hermione is brilliant: she's a great witch and a wise thinker. She's also much (much) more emotionally mature than either of her two boy best friends. When Harry can't figure out why Cho is upset all the time, it's Hermione who explains the complex feelings Cho has about dating Harry after Cedric's death at the end of Book 4 (21.186). And it's Hermione who is devious enough to think of a way to sway public opinion in Harry's favor, by manipulating Rita Skeeter into publishing an interview with Harry about Voldemort in The Quibbler, a tabloid newspaper out of the Ministry of Magic's control. Hermione seems to know everything, not just about magic and strategy, but also about people and politics.
Still, even if Hermione appears kind of perfect in Book 5 (certainly compared to poor Harry), she does have her blind spots. She is still so committed to the cause of house-elf rights that she starts leaving little hats and socks hidden under trash in the Gryffindor common room to try to trick the house-elves into picking them up and accepting their freedom. Dobby tells Harry later that all of the Hogwarts house-elves are so offended by these efforts to fool them into freedom that they have stopped cleaning the Gryffindor dorms entirely.
Poor Dobby – who is free, and happy about it – has started doing all of the cleaning himself so that he can pick up all of Hermione's knitted goods. Hermione is still so sure that she knows what's best that she refuses to listen to anyone who tells her that the house-elves at Hogwarts are happy and don't want freedom. Hermione can be stubborn as all get-out.
Hermione's flaws also emerge on the academic scene. This year is OWL year for Harry, Ron, and Hermione. All of the fifth years have to take their Ordinary Wizarding Levels, which are Ministry-administered standardized tests in each of the subjects taught at Hogwarts. Hermione loves school, and she also loves good grades. So, as the exams get closer, she grows moody and difficult to be around because of the stress of studying. In fact, Hermione always wants to talk over her own results endlessly. This can be miserable for other students (like Ron) who may not have done as well as Hermione.
Her intense focus on school also prompts her to give Harry and Ron ridiculous homework planners for Christmas that chant things like, "Do it today or later you'll pay!" (23.86). So, while Hermione may know a lot about magic and emotion, she's still not always perceptive about what the people around her actually want.