I'm being technical here. Once we grow into our skills it becomes difficult to break them back down to the beginning and do it gently and patiently for the learner. If you've played guitar for forty years and need to show a child how to form the triangle of a D chord your going to need to take a deep breath. This also applies to tying shoes. That's why not everybody is cut out for early childhood education. To remember not knowing is itself a hard core skill with many aspects. You have to grasp the content, obtain or make the material, prepare the environment and manage the social life of the class. And remember not knowing.
The hardest thing about teaching is bearing in mind not only what the other person doesn't know yet but also how it feels to not know. To not recognize an object or phenomenon. To not know its name or its parts or its actions. To not be able to use it. Basically to not be able to do anything but just touch it and start.