The rambling lecture that your headmaster gives you will actually be really, really important later on — e.g., "Now pay attention, Potter. This bird can carry huge weights, is naturally loyal, its tears heal wounds, and by pure coincidence its tail feathers went into your wand and your mortal enemies'. I wonder what use you could put it to, hmm?"
Isn't the real Aesop then "pay attention in class, 'cause a few items mentioned at some point during an entire school year might save your life"?
It's a good idea for an abused child to follow a seemingly kind stranger who then brainwashes the child into being part of a cult where people believe they can make "magic" with sticks.
When all your efforts towards a goal fail (not that you should try really hard in the first place), apply a mind-altering substance — it will give you all the correct answers, direct your actions along the only right path (don't bother to question either of those) and will even alter reality for your good.
Give children weapons that can kill/torture/maim people instantaneously. Just tell them not to. It'll probably be fine.
If a schoolyard brawl does happen to result in the maiming of a fellow student at your hand, then you can expect several hours of detention, causing you to, at worst, miss an intramural sports match. Your team wins the cup in your absence anyway, however, and you can still share in the celebrations, including a public make-out with your best friend's younger sister. The whole episode of the maiming is soon forgotten.
Loving your family is wonderful, unless you report an illegal secret society to the proper authorities in order to protect them. If you do that, you deserve to walk around with a disfigured face for the rest of your life.
Hey girls! The guy who sexually humiliates your best friend in front of the entire school to blackmail you into dating him will be an excellent husband to you.
Also, the guy who creepily inserted himself into your life, ruined your formerly close relationship with your sister, subscribes to a racist cult targeting you and is possessive about your wants and needs and refuses to accept that you loved somebody else and had a happy marriage, is truly in love with you and not an obsessive Stalker with a Crush who is Loving a Shadow and tearing you out of family photos so he could keep a photo of you for himself.
Stalking and acting like an entitled nice guy bastard makes you a good person, your creepy "love" for the woman you got killed will be seen as somehow redeeming of your overall nastiness to the point that the boy you abused for years will even name his kid after you and even calls you "the bravest man you ever knew" when all you did was follow the instructions of your deprogrammer and served as his errand boy and managed to barely succeed in your mission by pure luck. Being a horrible teacher and inconsiderate bully to kids who had it just as bad as you did, persecuting and outing a fellow teacher in a totally unprofessional manner, will magically be airbrushed away.
Journalists are jerks. Except those who believe in all conspiracy theories.
While we're at it: a bastard journalist you blackmailed is more reliable to transcript a story you dictate word by word than writing it by yourself.
Mind-controlling and torturing people is wrong, unless you're the hero.
You Guys! You're forgetting the most important one: 'It's easy to become a maniacal dictator who throws the world (i.e. England) into a Crapsack spiral. Kill anyone who defies you! However...you should probably stop at one-year-olds and loving mothers. They can, like, totally ruin your plans...by dying...and being a lovable infant...'
If the relationship between two pupils under your charge has deteriorated to the point that they're trying to seriously kill each other, resulting in a fight to the death that leaves one maimed, the most important lesson to teach the other is to remind him just how much you still hate his dead father.
If your specially-designed weapon for slicing people open is used by a student, it's the perfect time to go on about how horrible his father was.
If the person you used said weapon on was an enemy of yours, don't bother feeling too bad for using it. Even if he was having a nervous breakdown at the time you used it on him. And don't bother offering him your help while he recuperates. He was mean to you! He doesn't deserve your pity.
When you are told that some acts are so evil that doing it once result in life sentence in prison, they never mean it. Actually you can do it every single day, it's okay if you do it for greater good. And even if you do it for evil, it will be forgiven if you switch side at the last second. this refers to Dumbledore forgiving Draco, even if he used Imperium for a whole year.
Warping the warp: Go ahead and abandon a juvenile delinquent for an entire year. If you offer him a chance at redemption when it's too late for him to take it, you'll still go down in history as a good person, not a manipulative bastard who kept crucial information to yourself.
It's better to leave a child in an abusive home than to run the risk that he'll grow up to be proud, spoiled, or egotistical.
Because it's not like kids in abusive homes are people, prone to the same character flaws as the rest of us. It's completely impossible for a child in an abusive home to become negatively warped by the experience. Nope, every kid in an abusive home is an absolute saint.
Hey! A boy has a scar that gives him horrible pain? It's best to not remove it even if you knew how. Because your selfishness far outweighs a boy's comfort of not feeling like his own head is on fire and about to crack open from the inside.
Relationships that began when you were seventeen will always work out so that you are happy with plenty of children in twenty years. Also, your friends will never change, in fact it will be like the twenty years never happened except for said adorable kids.
Alternatively, if you're an author writing a Distant Finale, you better make sure your characters' friendships and romances don't break apart during the Time Skip or your fans will go apeshit and a coin a new termnote "getting rolfed", named after Luna Lovegood's offscreen husband in the finale for your treachery of daring to give your characters further development off-screen.
You should never be afraid to underestimate your enemies. Being evil will strip them of the very last shred of reason, imagination and the ability to learn from their mistakes.
School bullies and his/her friends will never, ever, not even when their lives are in chronic peril by some homicidal loon, decide to do the right thing and help out. They'll always try to sell out the hero. Therefore, it's okay to kick them out of the school without a second thought.
Not liking the Chosen One either automatically makes you a bad person or will turn you into one, no matter how justified your dislike of him is.
Alternatively, liking the Chosen One greatly increases your risk of injury or death, so you should probably keep your distance.
If you are an unpleasant female character than you deserve to be ravaged by centaurs. However if you are an attractive male villain you can get away with mind control and attempted murder and everyone will forgive you.
It's for the best for a young, impressionable child to be kidnapped by a secret cult society that's still stuck in the middle ages and be sent to a dubious "school" that doesn't even teach basic subjects like Math, Science, P.E., English, foreign languages... (unless you count severely mangled Latin.)
If the Big Bad is a result of you being a sanctimonious bastard and leaving a child with "dark tendencies" in an abusive household then the obvious solution is to do it again to another kid.
It's perfectly health for a society to be so isolationist they don't have the slightest idea of what basic technologies or clothing rules exist in the outside culture. In fact, play it for comedy: it's not creepy, it's funny!
Candies that induce hemorrhaging, vomiting, and severe swelling of the tongue are perfectly acceptable things to sell in a joke shop.
Harry Potter and the Prisoner of Azkaban:There's nothing wrong with accepting an insanely expensive vehicle as a gift from an anonymous stranger, especially when you have already pissed off some of the most powerful people around, and you know that such vehicles can be rigged to kill their driver. Those of your friends who treat such gifts with caution are just narks and deserve to be shunned.
Harry Potter and the Order of the Phoenix: So, you've got an adventurous and independent child who also happens to be a trouble magnet, has a murderous supervillain after him, has been known to act without thinking, and has been exhibiting pretty obvious symptoms of PTSD? Don't tell him any relevant details about what's going on in his life behind the scenes, ever. It's not like he'll try to find out on his own and end up getting into even more trouble along the way.
Harry Potter and the Deathly Hallows: Grand speeches about equality and coexistence with those different from you are fine and good, and you should be righteously indignant at and oppose those who display overt hatred and contempt for the different folk, but it's still probably not a good idea to actually expose your existence to those different people or cooperate with them, even when their lives and freedom are at stake, because in your heart you just know that they will want to exploit, abuse, persecute or exterminate you. No, that doesn't mean that the hatred and contempt against them is justified, and that you're a brazen shortsighted hypocrite.
The true way to hunt down the magic Soul Jar to take down the Evil Overlord isn't to appoint a secret force of competent professionals skilled in tracking magical objects, it's to leave it to the hands of barely trained school children. Never mind that their idea of investigating is camping endlessly, moving around randomly in various places in the vain hope that somehow they will come across the convenient plot clues, never mind that they conduct zany schemes that nearly compromise the whole mission and get themselves killed, or that they will get distracted from their simple task by pointless excursions (which you planted) that likewise nearly gets them killed. Eventually their luck will triumph over trivial matters of competence, resources and talent.
Remember, kids: Condescension and prejudice towards the handicapped is okay as long as you don't want to kill or torture them!
When faced with a diabolical madman bent on destroying those he deems to be worthless animals, absolutely, do not, EVER, under any circumstances, ask for help from those inferior sheep even during the very battle being fought to protect their rights.
Trying to start your own joke shop and make a little extra money for yourself is bad; promoting the use of date-rape drugs, however, is good.
Any attempts to abolish slavery will inevitably be deemed as laughably pathetic, so don't even try.
Treating your friends like dirt and walking out on them twice when they need you the most won't alienate them; if anything, it will only strengthen your friendship with them!
School sports and ensuring your victory over the other team at any cost is more important than being emotionally understanding.
Hiring a former terrorist to work at your school in a position of authority won't backfire in any way!
Your first friend is absolutely never wrong and remaining willfully ignorant to his faults makes you a good friend, until of course they call you "Mudblood".
If someone tries to kill you and seriously injures two other people in his attempts, just ignore it. There's no need to punish him in any way for nearly killing two people, or even to take any steps to make sure he doesn't hurt anyone else.
Discriminating people based on their heritage as opposed to life choices and personality is evil and terrible, as is drawing any correlation between heritage and magic. However, if a blood relative of yours commits a Heroic Sacrifice for their child, you and your home are automatically protected by that sacrifice, no matter how much of a jerk you are. Conversely, it doesn't matter how good friends you were with the person or how nice you are - if you're not related, the protection doesn't extend to you.
The Power of Love is incompatible with talent, hard work and merit. Even if you are a Idiot Hero with all your equipment handed down to you by your talented parents, even if you coast through with the help of your talented friends, and even if you lose badly in the only duel with a competent wizard free of magical handicaps, so long as you have all the requisite skills passed on to you by your dead elders and follow the plan handed down to you, your life will turn out okay. Just show your gratitude by naming your kids after all those dead guardians and surround yourselves with fellow underachievers, such as a Bookworm who never creates anything unique and a slacker who complains about his family all the time.
If you are an immensely intelligent man burdened with knowledge and responsibility, and devote your life to public service by bringing out the best in a whole bunch of screw-ups who wouldn't have amounted to anything without you, don't expect any consideration whatsoever. Expect to be called a Manipulative Bastard and recieve lectures from an ex-terrorist who badmouths you for raising a Tyke Bomb when said terrorist is responsible for the child being a Tyke Bomb. After all just because you tolerate endless slights all the time and provide second chances to an assortment of weirdos and rejects, doesn't mean you deserve any benefit of the doubt whatsoever.