Long before Airbnb persuaded strangers to sleep in one another’s homes and became a $25 billion company, it was just an idea to make extra bucks and make rent.

After their first guests, Airbnb’s founders realized they were on to something bigger than a stopgap for rent. They faced rejection plenty of times — and created their own version of Obama O’s cereal — but the three founders of Airbnb have built a big business in the past nine years.

Here’s how they turned their idea to rent out an air mattress into a business that has the hotel industry running scared.

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It started with an email. Joe Gebbia sent his roommate, Brian Chesky, an idea: What if they made a designer’s bed and breakfast, complete with a sleeping mat and breakfast? It was a way to “make a few bucks.” Almost nine years later that idea is worth $25 billion.

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Here is the email that started Airbnb. Shown onstage at #TED #TED2016 pic.twitter.com/A2ZF9Epcxj

In 2007, the two roommates living in San Francisco couldn’t afford to pay rent. The pair decided to turn their loft into an area that could fit three air mattresses. Along with the mattress and a night’s sleep came the promise of a breakfast too.

The pair knew a big design conference was coming to San Francisco, and it was making hotels hard to come by. They created a simple site, airbedandbreakfast.com, and bought three air mattresses. The duo had met at college at the Rhode Island School of Design, so they thought acting as tour guides to designers would be a fun way to make money.

See the rest of the story at Business Insider