Most PMs (85%!) manage several projects at the same time. Yet books and training courses focus on how to run one project, not how to combine and optimize your work to deal with more than one at a time.
Most project managers know and can cite the definition of project management, yet as evidenced by their project documents, discussions, and behaviors they do not know and cannot cite the stakeholder biases for the project. Worse, some project managers have no familiarity with the term.