I'm a sword guy. I spent over a decade training in historical swordsmanship (mostly European longsword - a mix of Fiore and Lichtenaur; but also a little kenjutsu).
There are so many bad takes about swords out there, but I think my personal "favorites" are about the folded steel technique used to forge katana.
See, to make a good sword, you need good steel which is iron + carbon. More carbon = harder steel. Harder steel is better for holding an edge, but also less flexible and more likely to shatter. All swords, European, Japanese or otherwise had to balance those concerns.
Anyway, in Japan, their katana forging technique used steel with slightly differing carbon amounts wrapped in layers in the blade. This layering had a couple of important metallurgical effects:
It gave the core steel a more consistent quality. Since the method they had of producing steel contained varying levels of carbon, the repeated layering, folding, heating and hammering evened it out.
The layering also increased the strength of the steel. By adding layers of high and low carbon steel, the sword smiths could control the flexibility vs strength of the core.
Ok, so without getting too deep in the weeds, that's (basically speaking) why katana were made of folded steel.
But I have been "informed" by so many people that folded steel:
Creates an edge like a thousand razor blades!
Makes katana stronger than modern steel!
Makes katana stronger than European swords! (steel-wise, it's a wash, though later blade geometry techniques like fullers arguably give European swords the - ha - edge in durability.)
In summary: katana are great - but not magic! The folded steel technique enabled forging swords of high-quality, consistent steel at a time when that was really hard to do. But that's it.
The whole McDonald's coffee debacle is constantly misreported, but I think it's becoming more known that McDonald's are in fact the bad guys in that one.
I used to work with this old guy. He was one of those dudes that was insufferable, but at work he was a semi-interesting story teller. But really it was because his desk was next to the back door exit. If you wanted to sneak out, you had to do it past his desk. And you had to be on his good side to avoid any leaky mouths…
Anyway, this one time I was sneaking out, it was summer. And he had the door open to let some fresh air in. In its place he had mounted a makeshift screen to keep the flies out. But this screen wasn’t quite tall enough and left the top foot of the door wide open. I had already seen a fly as I came down the hall, so when I saw his construction job, I’d found the reason…
So I said, “hey nice screen.” He says oh yeah, blah blah. Blah blah. Then I sort of point out the missing gap above the screen… he gets real serious and says:
“Flies can’t fly more than 6 feet off the ground.”
I had so many questions. What about flies on a mountain? What about flies inside a skyscraper? My head was salivating for more chunks of juicy knowledge from this guy… but alas I had my sneaky schedule to keep, and I said wow, cool. And left.
But the confidence from this guy could not be matched.
That the leader of a bee hive can't be female because the gods don't give women weapons, and that the drones can't be male because they take care of the young.
Not only did Aristotle writing this in Generation of all Animals cause misinformation around this to spread for literally centuries on end, including the presumed gendering of a 'king' leading the hive to be used to argue for a patriarchal dynastic monarchy as part of God's design - the wildest part is he acknowledged that other people were saying that the hive had a queen and the drones were male.
Dude was straight up like "some people say...but this can't be the case because of my commitment to misogyny which ignores things like lionesses existing."
A friend of mine was convinced that the "middle ear canal" goes all the way through your skull in a more or less straight line, connecting your ears. Y'know, because otherwise you wouldn't be able to hear sounds to the right of you with your left ear or vice versa. Maybe HE had such a thing where the brain was supposed to be...
That butterflies technically can't fly. But that they do proves there's a god, creating miracles.
Modern aeronautics can explain exactly how a butterfly can float in the sir.
Oh, the one random person from my childhood who said that black men looked like gorillas, which means they're stupid and violent. Mexican men looked like coyotes, which meant they're sneaky and conniving. And white men probably had a similar flaw, but since she was white, she didn't know what it was.
I'll add another bee one to the pile; I had a lady very confidently tell me that you don't see bees during the winter because they migrate. I wanted to correct her, but all I could think of was Monty Python. "Are you suggesting bees migrate‽" it's also hard to explain that they also don't hibernate, but create a sort of space heater around the queen.
“Fat is carbohydrates and people who don’t eat fat get carbohydrate deficiency which causes obesity. You need lots of carbohydrates to stay healthy, so eat fat!” - old man in my office block
Christopher Columbus hypothesized that he could reach Asia by heading west, landed on an entirely different land mass, and was so thoroughly convinced he was in Asia to the point of convincing the people who sponsored his first trip to sponsor 3 more trips. This was accepted as fact to the point that when someone else made the trip and acknowledged it as a new land mass, that new guy wound up having entire continents named after him.
That pandas are too stupid to survive or reproduce on their own. The truth is that breeders couldn't figure out the conditions for them to do it, and that we ignored the ways in which they are incredibly adapted to their environment.
Not only was this falsely shares but also harmful to the preservation of the species by poisoning public perception, and came as a direct result of yellow journalism and misinformation shared online.
For more info I recommend the book "The Truth About Animals: Stoned Sloths, Lovelorn Hippos, and Other Tales from the Wild Side of Wildlife" by Lucy Cooke
I said Google Glass was fake. I thought everything about it was true except the display. I had never encountered this kind of optics before so when they announced it I claimed it was not possible to ship that then. I was wrong.
A second cousin in the US put out a newspaper ad saying to vote for Trump as Biden was going to take away everyone's guns. He dedicated it to his baby granddaughter, who I assume will be very grateful for this when she grows up.