 You are going to eat more. The cookie jar effect is a powerful reason for companies to make larger and larger package sizes. And it's not just about snacks. For instance, you'll often see Brita water filters and electric toothbrush heads sold in these large multipacks. That's in part because manufacturers know that people forget to change those things. But if they can get you to stock tons of Brita filters in your closet, maybe you'll change them out more often.