[...] this is the one thing we have learned best predicts the success of founders in Y Combinator, is that every time we talk to a team, they've gotten new things done. That's the best predictor we have that the company will go on to be succesful."
Check out how to use the concept of Profiles and Propositions to better understand what your target market cares about, and the concept of Alternatives to better understand how they are currently solving their problems.
Be wary of an inability to identify alternatives to your solution. If people aren't using something else to solve the problem that your solution is designed to solve, it may be an indication that people don't sufficiently care about the problem to invest in having it solved.