When a magician watches a magic show he* sees something utterly different from the rest of the audience. While most of us are wondering how the conjurer made that elephant disappear, the magician is appreciating how the elephant appeared to be there in the first place. The same principle applies to an actor who goes to the theatre. He* will see the lighting, the smoothness of the entrances and exeunts, the clarity of the delivery, and the blocking. A show always looks different from backstage, and, once you have seen the greenroom, the set will never be the same again.
All of which is a long way round of recommending that you read this article by Stephen King on the Harry Potter novels. It's thoughtful and clever, and, most of all, it is one craftsman's take on the work of a fellow craftperson. Just click this link.
Another way of looking at it, is to say that it's the third highest earning author writing about the first.
Incidentally, I heard that somebody once asked Stephen King where he got his ideas. King replied "I have the heart of a small boy. And I keep it in a jar on my desk."
I have work to do.
*or she, or it.