What An Idiot / Harry Potter and the Philosopher's Stone

• The Dursleys swore to keep Harry away from the Wizarding World.
  You'd Expect: They'd raise him like their own son, or in a way that he is happy. If not because they are kind and nice people, or at least sane people (on the notion that Harry has literal wizards presumably looking after him and those might decide to pay a visit to the Dursleys if they don't treat Harry well), at least because making Harry feel welcome among them should be the best option for him to be less tempted to explore the Wizarding World if he ever does learn about it.
  Instead: They emotionally and (implicitly) physically abuse him, give him a cupboard to sleep in, and in general leave Harry with Dudley's sloppy seconds. Fortunately for them, Dumbledore and company doesn't check up on him (which is a separate point itself) not intervene after they find out about it.
  The Result: Harry is more than happy to leave them behind and enter the Wizarding World, to a degree that the memory of doing so is such a happy one, that it helps Harry produce his Patronus in the third book.
• A teacher is sent to introduce Harry to the wizarding world.
  You'd Expect: For Dumbledore to send any legitimately competent teacher or agent, preferably well versed in diplomacy and with good social skills, to tell Harry what he needs to know and gradually integrate him. Said individual would also pick up on the signs of abuse that Harry has endured and report this back to prevent said abuse in later books.
  Or: For that matter, Dumbledore could just do it himself and ensure that there are no screw-ups.
  Instead: Dumbledore sends Hagrid, a Manchild with No Social Skills who is barely a wizard at all. Hagrid completely overlooks the abuse that Harry has suffered, the Dursleys' blatant hatred of magic in general, and loses his temper, causing him to curse Dudley (who, Asshole Victim aside, still doesn't know any better due to his upbringing), which obviously doesn't endear Harry or magic to them and only leads to greater tension in the future.
• Harry receives his first letter from Hogwarts, and the first mail he's ever gotten. Before he can read it, Uncle Vernon confiscates it, and realizes what it is. He and Petunia have a hurried talk after Vernon tosses the boys out of the kitchen. Neither of them want Harry to grow up and become a wizard because they swore that they would "stamp out" any of the weirdness that Lily and James had when they took him in as a Doorstep Baby. The letter does say that you need to RSVP, which is a perfect loophole.
  You'd Expect: If they don't want Harry to attend Hogwarts, they would write back, as Petunia suggests, and say "NO". Cruel, but it should get them what they want. It turns out that Dumbledore (through Hagrid) bends the rules so that Hagrid can write in and just say he's picked up Harry, but the Dursleys don't know that. Petunia and Dumbledore have also corresponded before, so she knows he responds to letters.
  Instead: Vernon overrides Petunia and asserts that if they just ignore the letter then they can shut out the wizarding world.
  To Make Matters Worse: Petunia reluctantly goes along with this because she fears the witches and wizards.
  The Result: Hagrid and McGonagall are given permission by Dumbledore to use as much magic as possible to get Harry his letter. No matter what Vernon does, from sealing up the mail slot to changing Harry's bedroom, the letters keep appearing, and as Dudley puts it, "Daddy seems to have gone mad". Dozens appear over the days, and Hagrid tracks them from a remote hotel in the city to the rock on the island. The magic keeps finding them, and so does Hagrid.
• When Hagrid appears, he easily disarms Uncle Vernon, starts a fire in the grater, and cooks for Harry while educating him about Hogwarts. Hagrid is also a ten foot tall man who starts yelling at Vernon on learning that Harry knows nothing of the wizarding world.
  You'd Expect: After Hagrid ties his shotgun into a knot that Vernon would just keep his mouth shut. The jig's up, and Harry is going to be educated. You can't argue with wizards that can modify memories, and Hagrid is already shown to have a bad temper and is righteously furious on seeing how deprived Harry is.
  Instead: Each time Hagrid yells at Vernon, the man is momentarily cowed before he tries to insult Harry's parents, the Wizarding World, and Albus Dumbledore. And he tries to insist that Harry will not be going.
  The Result: Hagrid sarcastically tells Vernon, "I'd like to see a great Muggle like you stop him". He eventually goes too far by calling Dumbledore a "crackpot old fool". Hagrid wields his umbrella and uses magic on Dudley, giving him a pig tail.
• Dumbledore is aware that someone is attempting to steal the Philosopher's/Sorcerer's Stone, that they were good enough to make a serious attempt to steal it from Gringott's, and there's a strong possibility that it involves Voldemort.
  You'd Expect: Him to recruit former members of the Order to protect it, to surround it with spells that only let the right person past them and to keep its location a secret from everyone outside of that very small group of people. Hell, a Fidelius Charm would be enough, and Dumbledore has an extremely skilled Charms user on his payroll.
  Instead: He relies on less than competent people like Hagrid to supply guards and didn't quiz Hagrid on potential problems for those guards.
  Even Worse: His security used obstacles that were really less security and more puzzles.
  As A Result: Admittedly, some of them were tricky, but first year students were able to get past the same puzzles that were intended to stop a dark wizard controlled by Voldemort^note though Ron is known as an excellent chess player for his age, and when they reach the Potion puzzle, Hermione says that many great wizards lack an ounce of logic and would never be able to successfully pass through, so it has a bit of justification even if the whole thing remains a gigantic nonsense.. If not for the last spell cast on the mirror, you would have to wonder if Dumbledore was unconsciously trying to let Voldemort return to life. (Which is even possible, given Harry theorizes that Dumbledore wanted him to face Voldemort.)
  For that matter: Why keep the stone on school premises at all? They can literally Apparate anywhere on Earth, and instead it's kept in a school full of the next generation of magic users. Sure, it's one of the most well-protected places in the Wizarding World, but it is also intentionally placing hundreds of students in danger of getting caught in the crossfire, combined with the natural tendency of kids to go specifically where they are told not to, which is exactly what Dumbledore says at the start of the year: "Stay away from the third-floor corridor."
• After being insulted by Harry and Ron, Hermione runs crying to the girls' bathroom. Then, a TROLL! IN THE DUNGEON! appears, and the two boys realize Hermione isn't being gathered along with the rest of the Gryffindors because she is alone there and hasn't heard the warning.
  You'd Expect: Harry and Ron to tell the teachers that Hermione is in the bathroom. It might be awkward to explain them why she is there, but it's not like verbal bullying is especially punished in Hogwarts, and they can always claim she was just overreacting to a friendly joke (which is sadly used successfully as an excuse very often in the Muggle world), as it is up to her word against theirs after all. Even if not, despite all their previous actions, Harry and Ron still have enough smarts to conclude that risking being punished for making a girl cry is not a big deal compared to what they might suffer if it is ever found out they knowingly let said girl to die.
  Instead: They go to the bathroom entirely on their own, taking the risk of being found by either the teachers (who will give them at least a good reprimand) or the troll (who will try to crush their heads). Luckily, after a messy battle, who includes Harry and Ron somehow forgetting Hermione is in the room before trying to lock the troll there from outside, they manage to defeat the beast.
• Following the point above, Hermione is questioned by Professor McGonagall about her presence out of the group. Being now thankful to Harry and Ron for saving her, she intends to cover their shameful behavior.
  You'd Expect: Hermione to tell a half-truth and admit that she went to the bathroom to cry. When they ask about the reason, she could now lie and say that she was upset for getting a 99/100 in an exam or something equally in-character for her. Given Hermione's reputation at the school, nobody would doubt of this version and it would shut any possible student that witnessed her running tearfully beforehand.
  Instead: She makes up a self-blaming story, claiming that she snuck out intentionally because she thought herself capable to beat the troll. Aside from being a (fictional) act of stupidity, this is so atypical of a rule-abiding student like Hermione that McGonagall is doubly disappointed on her, getting her in serious trouble.
  The Result: While this makes the Trio all friends, McGonagall is full of Anger Born of Worry. She gives the trio five points total for bravery — five removed from Hermione and ten added for Harry and Ron— while telling them in the film they survived due to "sheer dumb luck".
• Voldemort, while possessing the body of Professor Quirrell, wants to kill Harry Potter without openly revealing himself so he can remain on-campus to steal the Philosopher's Stone.
  You'd Expect: That since he enjoys every possible advantage in this situation (Harry does not yet know he is a bad guy, Quirrell is one of Harry's teachers and in a position of authority over him, he is a fully trained wizard and Harry is an 11-year-old boy who is only beginning to learn elementary first-year spells), he would find it trivially easy to arrange to catch Harry somewhere alone and without witnesses and then murder him in any one of a myriad of possible ways that would plausibly look like an accident, or frame someone else for Harry's murder.
  Particularly: If he stunned Harry, then threw him into the room with Fluffy the Cerberus and let him get eaten, which would accomplish multiple objectives at the same time — it would kill Harry while making his death entirely look like "death by misadventure", it would politically disgrace Dumbledore that the Boy-Who-Lived died on Hogwarts grounds from a security measure set up by the school authorities, and it would force either Dumbledore or the Ministry of Magic to order the Cerberus removed from the school as a deadly hazard to students and thus remove the principal obstacle standing between Quirrellmort and the Philosopher's Stone.
  Instead: He tries to kill Harry by jinxing his broom during a Quidditch match...
  As A Result: ...which means his murder attempt is done in broad daylight, in front of hundreds of spectators, and in such a manner that Harry is literally not yet back on the ground before every observer with the IQ of a houseplant (all two of them) has figured out that someone is attempting to kill Harry Potter.
  Even Worse: Harry falls off his broom during Quidditch matches multiple times during later books and it's shown to be trivially easy for a member of staff in the crowd to cast a spell slowing his fall, meaning this method may not have been enough to kill him (or even hurt him) even if Quirrell had managed to knock him off.
• Snape realizes that Quirrell let the troll into Hogwarts as a distraction during the Halloween feast, to get the Stone. He goes and heads off Quirrell, but Fluffy bites him badly.
  You'd Expect: Snape would go to Madam Pomfrey and get his leg healed by magic. If Poppy can handle broken bones, concussions, and missing bones, she can heal a severe dog bite.
  You'd Also Expect: Snape would tell the other teachers (or at least Dumbledore) what happened and that Quirrell can't be trusted. Thus, either Quirrell can be suspended, the teachers can improve on the Stone's many protective barriers, or both.
  Instead: Snape doesn't in either the movie or the book. In the book, he gets help from Filch in the staffroom, that Harry happens to see, while in the movie he just limps while wishing Harry good luck before the Quidditch match.
  As A Result: Dumbledore's the only teacher suspicious of Quirrell, and the Magic Trio becomes convinced that Snape wants to steal the Stone.
• Draco Malfoy learns that Harry will be smuggling a baby dragon up to the school astronomy tower at midnight, and makes plans to get him caught.
  You'd Expect: Malfoy to either tip off Filch again, like he did for the midnight duel, or inform another member of staff about what Harry's up to (such as his head of house, Snape, seeing as how they both share a mutual hatred of Harry).
  Instead: Malfoy decides to lie in wait for Harry at the entrance to the astronomy tower, despite having no way of catching Harry by doing so, and putting himself in danger of being caught out of bounds.
  As A Result: Draco gets caught and punished by Professor McGonagall. In the film he also does this, but the professor punishes him for being out of bed at the time.
• Harry, Ron, and Hermione tell McGonagall their suspicions about "someone" being after the Stone. Harry is about to say "Snape" but since there's no proof backtracks to "someone".
  You'd Expect: McGonagall to immediately haul them into her office and demand exactly what they know about the Stone and how they know it. True, she may believe that they are talking nonsense, but if you are helping to guard a life-or-death secret, and eleven-year-olds are able to discuss the secret, nonsense or otherwise, then you have a major security leak and should try to find out what is happening. Had McGonagall acted sensibly, she could have found out, not only that Hagrid had let things slip in front of the kids, but that he did the same in front of an unknown party. Also, she could assure her students that she would take higher security measures, because Harry and Ron faced the troll to save Hermione without getting a professor and could go Leeroy Jenkins again.
  Instead: McGonagall refuses to believe the Stone is in danger and sends the kids on their way, threatening them with punishment if they don't butt out, and unwittingly making it necessary for them to go after the Stone themselves.
• Rejected by McGonagall and learning from her that Dumbledore is away, Harry deduces that Snape will choose that night to act. Accompanied by Ron and Hermione, he sets out for the Stone's chambers, where they find out that someone has entered and passed the first traps.
  You'd Expect: Having now physical evidence of a thief inside (the harp, the damaged key, the troll knocked out), Harry and company to return and warn McGonagall. She will be surely irate at them for disobeying her previous orders, but their discovery entails that a thief has been caught red-handed and is probably still in the chambers, where McGonagall and the other teachers can arrest him (or at least contain him until Dumbledore returns), so this should give the kids a well-deserved break. Yeah, they are wrong on the baddie being Snape, but this point, if mentioned, should be irrelevant once the teachers ascertain someone has really broken in. Sending an owl to Dumbledore before telling McGonagall might be useful just in case she still shows unreasonable, as well as desirable for a matter of time, especially given the suspicions that Voldemort is involved. At the end of the process, with a bit of luck, Voldemort himself might end up caught alive.
  Instead: Nope. Harry decides to follow the thief and somehow get the Stone before, even knowing that they are no match for a Hogwarts teacher in a duel. The possibility of actually reaching the villain would achieve nothing aside from getting the kids killed or held hostage, but this is never even considered. In turn, the idea of warning Dumbledore by owl actually does up to them twice, but they only execute it being already deep into the traps and facing mortal danger, to the point Harry sends Hermione to contact Dumbledore just before he confronts the thief in the last room - thus not giving Dumbledore any time window to arrive.
• In the book's climax, the Philosopher's / Sorcerer's Stone has ended up in Harry's pocket, and Voldemort and Quirrell know this. Quirrell, as described above, is a fully trained wizard, and in this scene he's been casting non-verbal wandless magic, marking him as one of the most powerful wizards we see in the series.
  You'd Expect: Quirrell to try and get the Stone by magic. Even if Rowling hadn't thought of Accio or Imperio (a summoning spell and a mind-control spell) yet, Quirrell could just kill him by magic and take the Stone from his corpse. He is, after all, a wizard — magic should be reflexive for him. And despite Harry's protection, it is clearly shown that magic does work on him, such as the ropes Quirrell conjured; just making the ropes reach for his neck and strangle him should do fine. As will be noted again later on, a modicum of creativity would have allowed him to kill Harry easily.
  Instead: Forgetting about magic altogether, Quirrell runs after Harry and grabs him physically, getting burned by the magic love protection in his skin. Even after this ugly turn of events, he tries again, now trying to strangle Harry with his hands, but obviously fails for the same reason.
  As A Result: By the time Quirrell gets the idea to use magic (because Voldemort is screaming at him to), it's too late as Harry burns him to death.

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