Legendary fund manager Peter Lynch once said that you shouldn't invest in any idea you couldn't illustrate with a crayon.

Though I'm not much for crayons, I do love the pithiness of that line. We regularly preach the same idea at the Fool: Don't buy what you don't understand. And if you can't simply sketch out a company's business model -- how it actually makes money -- then maybe you shouldn't be investing in it.

It's a pretty safe bet that when you run through your morning routine, you probably use a Johnson & Johnson (NYSE: JNJ) product. But the company does so much more than keep us squeaky clean and ouchie-free. In fact, it might surprise you to learn exactly how Johnson & Johnson makes the majority of its money. Let's take a look. (Note: I'm focusing on revenues here, not earnings.)

Sources: Johnson & Johnson 2011 10-K and www.jnj.com.

Think I missed something in this illustration? General thoughts on this exercise? Let me know in the comments section below. And if you haven't already, be sure to follow our Johnson & Johnson news and commentary using the Fool's free new My Watchlist tool.

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.