According to piaget’s theory of cognitive development we actively construct our cognitive world using

We actively construct knowledge about the world by exploring and interacting with it. That means that we can know the theory about something but until we try it we won't know how to do it. That's how children work. You can tell them how block building works but until they start building blocks themselves they won't know how to do it. Same when you're an adult. You can read a book about car fixing, but you won't know how to do it until you open the car and start working on it.