Insomnia is a gross feeder. It will nourish itself on any kind of thinking, including thinking about not thinking.
But things such as 'Harry Potter', all I can do is shape my character, seek the director's approval on that, and basically take it from there. Professor Flitwick in 'Harry Potter', I kind of defined how I saw him from reading the book, and luckily that matched up with the director's vision.
If you cut down a forest, it doesn't matter how many sawmills you have if there are no more trees.