I've never wanted to be a witch, but an alchemist, now that's a different matter. To invent this wizard world, I've learned a ridiculous amount about alchemy. Perhaps much of it I'll never use in the books, but I have to know in detail what magic can and cannot do in order to set the parameters and establish the stories' internal logic.
J. K. RowlingAn Unbreakable Vow?" said Ron, looking stunned. "Nah, he can’t have.... Are you sure?" "Yes I’m sure," said Harry. "Why, what does it mean?" "Well, you can’t break an Unbreakable Vow..." "I’d worked that much out for myself, funnily enough.
J. K. RowlingSlowly, very slowly, he sat up, and as he did so he felt more alive, and more aware of his own living body than ever before. Why had he never appreciated what a miracle he was, brain and nerve and bounding heart? It would all be gone...or at least, he would be gone from it. His breath came slow and deep, and his mouth and throat were completely dry, but so were his eyes.
J. K. Rowling