If there's one thing I've learned in my short and tumultuous time as a product manager is that, ultimately, it's just about giving a shit. That and having somewhere good to go. That is, having a vision and inching towards it, sprint by sprint, week by week. It pains me to use this word, "vision", but there really isn't any other word for it. How much do you manage? As little as possible if you ask me. How do you motivate people making this thing you're in charge of? You shouldn't have to. If people care, you don't need to motivate them. Take the now famous example of Valve Software the games company who literally let's you work on whatever you want firm in the belief that people who care about their work, do good work. And good work sells. So basically, get out of the way and let good people do what they do well.
For all this though you need to let go a little bit. This is extremely hard for us art school types who've had our minds filled with visions of superiority and genius. But its got to be done, because this is the real world. In the real world there are products, projects, cities and novels that all live and die not by their design, but by how well the good people putting them together are all moving in the same direction.