Editor’s note: The following is an excerpt from a new book written by Shirish Nadkarni, a Seattle tech veteran who co-founded Livemocha (acquired by RosettaStone) and TeamOn (acquired by BlackBerry). You think you have come up with a brilliant idea for your startup. You have spoken to your friends and colleagues, and they think that the idea has merit. You have even done the preliminary market research and spoken to many potential customers, and feedback has been positive. But how do you really know that it will form the basis for a great company?