Here’s an experiment you can try at home: Choose a pop song—any pop song at all—and use your index finger to tap it out on a desk for a colleague. No humming along, no accompaniment at all. Just your finger tapping out the melody. You are the tapper. Your colleague—the listener—has to figure out which song it is.

What are the odds she’ll get it right?

In a keynote speech at lunch today, Chip Heath—who co-authored Made to Stick with his brother Dan Heath—says someone took the time to conduct a study on this very topic. And it turns out that tappers give it a 50-50 shot. Sounds reasonable, right? But the tapper—who hears the song in his head—might be surprised to learn that only one in 40 listeners can correctly identify the song.

Heath calls this the curse of knowledge, and says the same principle applies to marketing. When you have a comprehensive understanding of your product or service, it’s all too easy to tap something out and assume your listener gets exactly what you mean. When she doesn't.