Chemistry teachers start with such confidence! "The octet rule is absolute! Atoms want 8 electrons in their outer shell!" Then comes the inevitable backpedaling when students learn about the exceptions...
Hydrogen: "I'm good with 2."
Transition metals: "We'll take 18, thanks."
Boron: "5 is my lucky number."
Xenon compounds: "Rules? What rules?"
It's like teaching kids that Columbus discovered America, then spending the next 10 years explaining why that's completely wrong.