If, with Pringles "once you pop, you can't stop", why do they give you a lid?

This has always boggled me so I have turned to the web to find my answers. First I tried the Pringles web site but there was nothing on it about their reasoning for the lid. Once upon a time, I asked this girl I had jus met in a club, I didn't see much of her after that. Everyone I ask thinks I'm bonkers!!! Please help?