Great startups are often based on an idea that most people refuse to believe is possible at the time it appears. Take these examples:

Twitch: Millions of people will tune in to watch other people play video games online.

SpaceX: It’s possible for a founding team without significant space or rocket experience to build a company that makes manned space flights better than NASA or any other government on the planet.

Airbnb: Hundreds of thousands of people will be willing host strangers in their homes, even though those strangers may be murders or thieves. And millions of travelers will prefer those homes over an nice hotel.