Rowling says she’d never felt such a rush of excitement, knowing the story would be so much fun to write.
There was a glitch, however. Rowling didn’t have a writing utensil that worked, which never would have happened under normal circumstances. After all, she was a writer.
So, Rowling took the disruption and used it to her extreme advantage.
With the characters of Harry, Ron, Nearly Headless Nick, Hagrid and Peeves bouncing around in her mind, Rowling was forced to sit there and think about the characters and their story. And that, she says modestly, “was a very good thing. I was besieged by a mass of detail and if it didn’t survive that journey, it probably wasn’t worth remembering.”
— Adapted from Success, J. Pincott, editor, Random House Reference.