It's always surprising to find out how much you think you know that you actually don't. There's so much assumed knowledge out there that just gets passed along without checking the accuracy first. It happens every day. You overhear somebody trying to show off at a party, hear it repeated later, and maybe a TV show throws the same "factoid" out there, and presto, misinformation spreads, now shining like real information—only it's fool's gold.
So don't feel bad if you didn't know some of these things. Common knowledge is commonly misinformed, so lots of people have been hoodwinked. The fact is, everybody should know these things, but few people do.