Art, not Science
With all the science for project management hanging around your neck (think PMBOK), try to remember that successful project management is really an art, not a science. It is the art of managing others to get them to do what you know needs to get done. It doesn't matter how well you know how to track requirements, manage risk, etc.; it's about how successful your team is against the goal before them. Use the (scientific) tools to your advantage, not as your hammer.