I'm not sure that's a completely accurate analogy either. When you're using a VPN people can still see that you are sending traffic through your tunnel, they just can't tell what it is that you're sending. It's like looking through frosted glass; there's definitely something moving in there but you can't tell what.

I suppose the best way to describe it is you send a locked box to a trusted friend; everyone handling it can see the box but can't tell what's inside. Inside the box is a letter, your friend posts it so it looks like it came from them. Your friend then gets a reply, puts it in a locked box, and send it back to you. Nobody between you and your friend can snoop on your mail but anyone between your friend and the final destination can.