In $2007,$ Joe Gebbia and Brian Chesky realized they could not afford the rent on their pricey San Francisco apartment, so they decided to put an air mattress in their living room and offer people an alternative to an expensive hotel room. This is the story of how Airbnb got started. In other words, Airbnb began when Gebbia and Chesky $\_\_\_\_\_\_\_\_$; the company grew because they $\_\_\_\_\_\_\_\_.$