All too often, people look at a startup and assume that the key to its success was coming up with the right idea to disrupt a market. Not true. The truly groundbreaking startups all have something else in common: a willingness to keep rethinking what’s made them successful. Take Uber. Ride-hailing is a brilliant idea, sure. But the company has moved beyond its initial value prop, customized its product for different markets, and executed some…