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. RowlingSeverus, please fetch me the strongest truth potion you posess, then go down to the kitchen and bring up the house elf called Winky. Minerva, kindly go down to Hagrids house where you will find a large black dog sitting in the pumpkin patch. Take the dog up to my office, tell him I will be with him shortly, then come back here.
J. K. RowlingWhy canโt I drink the potion instead?โ asked Harry desperately. โBecause I am much older, much cleverer, and much less valuable,โ said Dumbledore.
J. K. Rowling