What still confuses you in your adult years, that you're usually embarassed to admit?

It’s okay, you’re among friends here and we won’t laugh. Much.

I’m embarassed to admit that I still feel horribly confused about how uber heavy metal ships are able to float. It’s been explained to me about water displacement, but God help me, I still don’t understand how something so damn heavy and made of metal doesn’t sink.

What do you still feel confused or baffled about, even if it’s been explained to you?