Founders

Startups often don't have to be the first to come up with a new idea. Carpool services and room-sharing services existed before Uber and Airbnb. Search engines existed before Google. But they were different from the existing solutions in a meaningful way. 

For example, Google's main goal was not just to build search engines. It was "to improve the quality of web search engines" in a scalable way. They were aware of the problems in the existing search engines, and addressed them in their paper: 
http://infolab.stanford.edu/~backrub/google.html