How do you talk about a product before anything like it exists? How do you guide the engineers building it and the marketing department who has to sell it? As co-creator of the iPod and iPhone, founder of the learning thermostat Nest, and with over 300 patents to his name, Tony Fadell is a serial entrepreneur who now focuses on investing. He tells Azeem Azhar how he uses opinion-based decision-making in his work, and why thinking like a product manager helps drive radical innovation.