The answer: basic math.

Since its introduction in 1972, McDonald’s Quarter Pounder sandwich had been one of its most popular menu items. The name comes from how the meat patty weighs a quarter of a pound (or four ounces) before cooking, much larger than the two-to-three ounce patty used on the chain’s regular hamburgers. In 1980, A&W tried to up McDonald’s by offering an even bigger, meatier burger: the Third Pounder, made with 1/3 of a pound of beef, and priced about the same as a McDonald’s Quarter Pounder. Market research and focus group testing indicated that customers would flock to A&W for the new burger, but it ultimately flopped. Confused, A&W sent corporate representatives to interview A&W customers. The findings: customers thought that a third of a pound was less than a quarter of a pound, and that they were getting ripped off by paying the same for less meat than they would at McDonald’s.
Almost 20 years later, that marketing and math mistake had been long forgotten. With big fanfare and a launch on the Today show, in 2007 McDonald’s introduced the Angus Third-Pounder. Not so surprisingly, the burger—the biggest McDonald’s offered—was off the menu in a year. Perhaps the company thought that “Angus” was the troublesome word (it’s a type of high-quality beef). In 2015, the company unveiled the Sirloin Third Pounder. That one didn’t last either.