Also, when someone says, "they knew the earth was round in the Middle Ages", they mean "educated people knew". Guess what fraction were educated? Not many. So .

Also, when someone says, "they knew the earth was round in the Middle Ages", they mean "educated people knew". Guess what fraction were educated? Not many. So ... averaged over the population, it's not entirely correct. It would be like saying, "It's a myth that in the 21st century, they were bunch of rubes who were unaware that every single object is exerting a gravitational force on them." Well, um, it's a myth that physics-educated people were unaware of this, sure. But most people have no reason to learn about this or be aware of it; it's not relevant to everyday life.