From Red Herring:
The key distinction is between failing and losing. Failing means getting blocked on an intended course, backing out, and restarting. Losing means persisting in your failing ways, refusing to change your current course, and instead putting significant effort into justifying the course. Worse yet, it means getting defensive whenever you are challenged about your vision. In high-tech ventures, you can expect to fail many, many times. That’s part of the deal. You get up, brush yourself off, and get back in the game. But lose just once, and you may never have another chance. That too is part of the deal.