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New York Mayor Bloomberg’s new rules limiting sodas and other sugary drinks sold in restaurants, movie theaters, sports arenas, food carts and delis to 16 ounces has spurred a national debate. Should government limit our serving sizes? Bloomberg’s rules do not prevent a person from buying two, five or 10 16-ounce sodas and drinking them all in one sitting. They just prevent a restaurant from selling that much soda in one cup. Stupid rule? Not if you know the history of supersizing.

The idea can be traced back to a man named David Wallerstein, who ran movie theaters in the 1960s. He tried method after method to get his customers to buy more than one order of popcorn. Nothing worked. Then he realized why: people thought they would look like pigs if they bought two popcorns. So he tried increasing sales a different way, by offering a jumbo size popcorn. The trick worked. Popcorn sales went up.

Nowadays, this profit-boosting trick is the standard at any movie theater. Some theater chains require cashiers to inform every customer that they can have the next size up for an extra quarter or two. It’s a tiny amount of money to pay for a larger size of soda or popcorn, but for the theater, those extra few cents are nearly all profit. The labor costs them the same to sell you a small popcorn or a large one. The added cost of a box or a cup plus some syrup and water, or some popcorn, salt and seasoning is minimal. And you as the customer perceive this as a great value.