What started as a marketing gimmick by a man who owned two Subway franchises in Miami has turned into a national phenomenon and pumped up the restaurant chain’s profits, said an article in Business Week.

Stuart Frankel decided to offer $5 footlong sandwiches on Saturday and Sunday, which was about a dollar less than the regular price. “Plus I like round numbers,” Frankel told Business News. And suddenly, he had lines out the door.

Other franchisers were wary to adopt the promotion because they thought it would drive up food and labor costs, negating any profit. But some individual restaurants created their own $5 footlong campaigns and saw the number of customers, and profits, soar.

The national Subway headquarters finally picked up on the idea, built a catchy ad campaign around the $5 footlong and generated $3.8 billion in sales from that concept alone, proof that the best ideas can come from small places.