re: What's the simplest thing you've had to explain to a full grown adult?

I've had to explain scarcity to someone with a master's degree. She didn't understand why poverty wouldn't end if you just gave everyone a million dollars. I had to show her pictures of Zimbabwe currency and everything.

We live in the eastern time zone. I've had to, repeatedly, tell a friend of mine that New York, DC, Baltimore, etc aren't on a different time.

One of my most-frustrating was during the movie ID Thief with Jason Bateman. There's an establishing shot that says "St Louis," but it's clearly Chattanooga. The aquarium, Ross's Landing, everything are there, plus a digitally rendered Gateway Arch. My buddy's wife (who is born and raised in Chattanooga) got really mad at me when I told her that it wasn't St Louis. She swore that "they can't put it in a movie if it's not true."