To be sure, entrepreneurs in highly specialized and technical industries need the knowledge that only users (doctors, lawyers, engineers, and the like) can provide. Doctors understand what other doctors will value in a new product; lawyers know what other lawyers need. But you can have too much of a good thing — including input from such experts. In fact, my colleagues and I have found that innovation thrives when expert users make up about 40% of an invention team. Any less and the company will lose sight of what its customers need; any more and the group will tend to converge on old ideas.