English is chock-full of expressions that we commonly use without any knowledge of where they come from (like "chock-full"). I'm not saying it's a problem--speakers of English tend to figure out what they mean from context, and as long as we understand each other, there's no cause for concern. But I find knowing the origin of idioms makes seeing and using them a richer experience.
For example, I heard someone the other day mention that he was, “waiting for the other shoe to drop." I knew exactly what he meant. He was anxious about some inevitable, impending event. Something had occurred that seemed to entail an unavoidable consequence. It might have been something like,
The boss announced after the budget meeting that layoffs in our department are likely. Now we’re all waiting for the other shoe to drop.
As with many idioms, the origins of waiting for the other shoe to drop are a bit hazy, but the consensus is that the expression comes from an old joke that might have been part of a vaudeville routine.
A man comes home late to his room in a crowded boarding house. As he gets ready for bed, he removes a shoe and drops it with a thump on the floor. Remembering that his downstairs neighbor often complains of late-night noise, he takes off the other shoe and puts it down gently. After he settles under the covers, an irritated voice from the apartment below shouts, “When are you going to drop the other shoe?”
It's not a great joke, I have to admit. But it explains the expression.