Via Buzz Anderson, the story of how the credit card was thought up:

In 1949, Frank McNamara, head of the Hamilton Credit Corp., went out to eat with some of his buddies. At the dinner were Alfred Bloomingdale (grandson of the founder of Bloomingdale’s department store) and Ralph Schneider, McNamara’s attorney. The three men ate at Major’s Cabin Grill- a famous New York City restaurant located next to the Empire State Building. At the end of the meal, McNamara reached for his wallet and was shocked to discover he’d forgotten it. He called his wife to bring him some cash and rescue him from embarrassment. McNamara vowed never to let this happen again. So he came up with the innovative concept of a card that could be used at multiple locations – with a middleman (Diners Club) between restaurants and their customers. In early 1950, McNamara issued 200 Diners Club cards to his associates who often went out to eat with clients. At that time, the cards were accepted at 14 New York City eateries. A customer could eat without cash at any restaurant accepting the cards. Diners Club would pay the restaurant and the cardholder would repay Diners Club.

The best business formulas come from identifying a need based on a personal experience and being able — through a combination of luck and skill — to satisfy that need. There, I just saved you four years of business school.