It's easy to understand that as an object is lifted, it gains gravitational potential energy; as it falls, that potential energy is converted into kinetic energy. But what about when it's at rest? If a book sits on a table at rest, gravity exerts a force on the book. But the exertion of force requires energy, right? And what about the normal force? It exerts force as well; where does the energy to exert THAT force come from? Am I misunderstanding what energy is?
EDIT: Question answered - humans have a flawed understanding of force, and force actually isn't conserved in nature like energy is.