Things you learned in English class...

...that turned out to be bullshit in real life.

My teacher always told us that:

*Things don't happen at night, they happen by night
*You don't live a life, you lead a life

While you can lead a life by night, I've learned that most native English speakers (especially Americans) would live a life at night instead.

What other things not completely in touch with reality did you learn in your English/any other language classes?

Here's a puzzler: how is it that the words "suck" and "blow" can have both opposite meanings, i.e. "The vacuum sucked up the dirt." and "The wind is blowing hard today.", yet also are synonyms for fellatio. Pardon me, but what the hell were the people who invented that particular slang term thinking?