Hermione Granger is one of the most popular literary characters of all time. She is the female protagonist and one of the leading characters of the Harry Potter series. She is also considered the brightest witch of her age and has helped Harry and Ron out of numerous scuffles throughout the franchise's history.
If it weren't for Hermione, there is every chance that Harry and Ron would have died a long time ago, or at least gotten themselves into way more trouble then they already did. Hermione has had her fair share of genius moments throughout the series, but she has also had a few not-so-genius moments too.
10 Genius: Hermione managed to solve Snape's potion logic puzzle.
Back in the first book of the series, Hermione proved her prowess as both a witch and as a logical thinker when she completed Severus Snape's complicated potions puzzle. Hermione comments that many witches and wizards are not good at logic since they can typically have magic do everything for them.
Because of this, many would be trapped in the chamber forever. Before Harry can panic, Hermione assures him that she isn't one of those people. Even as a first-year, Hermione proves her incredible intellect by solving the logic and getting her and Harry through their respective doorways unharmed.
9 Not Genius: Attempting to trick the house-elves into freedom.
Hermione's mission statement and intentions with S.P.E.W. were certainly coming from a good place, but in execution, they didn't play out quite so well. There are definitely some house-elves who would do anything for freedom and who deserve it after being mistreated by their masters, such as Winky and Dobby, but there are just as many house-elves who are content to work and don't mind doing so.
Hermione tries to trick them into freedom by sewing little hats and clothes for them and leaving them around the Gryffindor common room (since that is the only way a house-elf can be set free). Eventually, they just stop cleaning the common room and only Dobby does it since he is a free elf already.
8 Genius: When she figured out the monster within the Chamber of Secrets.
In the second book of the series, Slytherin's heir opens the Chamber of Secrets once again and unleashes the horror within. No one knows what monster roams in the chamber, only that its goal is the purge Hogwarts of all they deem unworthy, ie Muggle-borns. Hermione is the only person to put two and two together and figure out the creature in the chamber and how to find the entrance.
Unfortunately, before she is able to tell Ron and Harry, she gets petrified by the Basilisk. Luckily, Hermione was smart enough to write a hint on the Basilisk paper, keep it on her person, and use a mirror to check around corners. She saves both herself and Penelope Clearwater from death by doing this even though she does get petrified, she ultimately saves the day.
7 Not Genius: Using cat hair in the Polyjuice Potion.
Accidentally being turned into a cat is not one of Hermione's finer moments. In the second book, Hermione, Ron, and Harry drink Polyjuice potion so they can get into the Slytherin common room and question Malfoy, believing him to be Slytherin's heir.
Unfortunately, Hermione mistakenly took cat hair off of Millicent Bulstrode's robes and the transformation went terribly wrong. It's a little hard to understand why she wouldn't have noticed it was animal hair, which is much different in appearance from human hair, but she probably didn't think about that at all when it happened.
6 Genius: When she blackmailed Rita Skeeter.
Rita Skeeter was a thorn in everyone's side when she was introduced during the fourth book of the series. She consistently wrote terrible things about people in the wizarding world's version of trash journalism and tabloid gossip.
Harry was badly affected by the content she published, as was Hermione when her name was also dragged through the mud. Hermione eventually figures out that Skeeter is an animagus, which is how she was able to learn such dark secrets about people. She traps her in a jar and blackmails her since she is an illegal animagus and keeps her from writing anything untoward in the future.
5 Not Genius: Tricking Umbridge into the Forbidden Forest with the centaurs.
To be fair, Hermione was thinking fast, on her feet, and doing her best to keep everyone alive without betraying the Order of the Phoenix or Dumbledore's Army, but bringing Umbridge into the forest was probably not the best decision. It could be that Hermione was actually intending for Umbridge to tangle with Grawp but they wind up meeting centaurs.
Having the centaurs do their bidding enrages the creatures and Harry and Hermione almost follow Umbridge down a dark path before Hagrid's half-brother Grawp intervenes. The entire scenario when south very quickly.
4 Genius: Hermione packed ahead of time for a quick getaway in Deathly Hallows.
One of Hermione's most brilliant moments in the entire series is when she is readily prepared for her, Harry, and Ron's road trip to hunt down Horcruxes in the seventh book. Bill and Fleur's wedding is interrupted by a frightening message about the Ministry falling and shortly after the wedding is overrun with Death Eaters.
The golden trio barely manages to escape in time. Luckily, Hermione had her nifty magical bag full of everything they would need to be prepared ahead of time as she feared something like that would happen. Her preparedness certainly helped them get a better start on their journey.
3 Not Genius: Her obsession with Gilderoy Lockhart.
Considering how young Hermione was in the early books of the series, you can't really blame her for having a crush on a handsome and supposedly talented wizard like Lockhart.
However, it's a little strange that her obsession persists even after Lockhart's embarrassing pixie debacle and his fascination with Harry. At some point, it appears she may have just been in denial about someone she idolized turning out to be such an idiot and a fraud.
2 Genius: Using a Stinging Jinx on Harry's face when they got captured by Snatchers.
Hermione's intellect really shines in the seventh book of the series which is saying something as they weren't even in attendance at Hogwarts. It really proves that Hermione was a genuinely skilled witch and not just a good student. At one point in the book, Harry accidentally triggers the Voldemort taboo and the trio gets kidnapped and taken to Malfoy Manor.
The second Hermione realizes what Harry has done, she shoots him in the face with a Stinging Jinx to disfigure his face. This keeps the Snatchers from immediately recognizing Harry Potter and likely helped keep all three of them alive as they were taken to the manor first.
1 Not Genius: Taking way too many classes.
In book three, Hermione tries to take on way too much at one time. She decides to take a ridiculous amount of classes and ultimately winds up getting so overwhelmed she has to take a Time-Turner to go back in time and ensure she can get to class on time.
One of Hermione's faults is trying to be the best at everything. She quits Divination because she can't master it, she gets jealous of Harry's Defense Against the Dark Arts scores, and she also gets jealous when Harry begins succeeding in Potions due to help from the Half-Blood Prince.