How Do You Write a Book?

I understand you took a class at Harvard Business School when you were writing free fruit and millionaires because your main character Casey was a milliner. You took an entire semester at the Fashion Institute of Technology to learn how to make hats. I think that again, it goes back to confidence. I feel a sense of authority in what I write. But by the time I finish writing a book, I know so much about that field. And for me, those characters are very real because they are composites of interviews that I've had.