Mason Wartman had a comfortable job on Wall Streetin New York City and was earning very well. But there was something missing in his life. Pizza! Well, not quite, but he had always dreamed of owning his own business. So he quit, moved to Philadelphia and opened Rosa’s Fresh Pizza.

Then, one day, a customer did something that would change Wartman’s business – and his life – forever. A man walked into the $1 pizzeria, ordered a slice for himself and asked if he could buy a slice for a homeless man.

“I said, ‘Sure,'” Wartman told National Public Radio. “I took his dollar and ran out to get some Post-it notes and put one on to show that a slice was purchased.

This system of “paying it forward,” so to speak, became a phenomenon in Philadelphia. Over the next year, customers bought more than 10,000 slices of pizza, which were given for free to the homeless or others struggling to make ends meet.

Customers left notes all over Wartman’s wall. The notes are filled with messages of inspiration and appreciation.

Now Wartman helps feed nearly 30 to 40 homeless people a day, and the goodwill is inspiring similar trends at other restaurants, including Starbucks and Panera Bread. It has also caught the attention of national media, which in turn attracts more people, which in turn means more donations.

Wartman believes that people generally want to help, but often do not know what they can do.

“This is a super easy way, a super efficient way and a super transparent way to help the homeless,” he said. “They are just really nice people, you know? Sometimes homeless people buy them for other homeless people.”

“Everyone wants the world to change, but in order to do that, we have to change ourselves,” one customer remarked appreciatively.

Who would have thought that would only cost us a dollar?