It wasn't that difficult to come up with an outline for the book. But it wasn't easy to follow the outline, though! 😉 Once I started writing, I soon realized that I had to allow my creative mind to write without limiting it to the outline. After I wrote a big portion of the book, I started editing it and making it fit into the outline. I was advised by my editors to delete one of the chapters, and to modify the title of a few other chapters. It was a lot of work to edit it, and to move chapters around, but we were able to do it.
When I met with the first editor to get her comments and edits, she suggested that next time I write a book, I should write an outline before I start writing it. I told her that I had an outline; I just didn't follow it every time I wrote!