I was a little taken aback by the question. It was a little like somebody asking, what makes you think you can invent the telephone or climb Mt. Everest or solve world poverty. Writing a book isn't a hard thing at all when it is the one thing you really want to do. Millions of people write books. Many write several books. Agatha Christie wrote gazillions and each was individual and delightful and intriguing. I am just writing one book and it has been the most wonderful experience.
Initially, I wanted to write a book on solution-focused therapy based on the work of Abraham-Hicks, but it became a dry text book and I got bored with it so I stopped. Then I read a wonderful book called Tell to Win which described the human love of story, so I decided to write a novel, which at first felt like I was giving up on my dream, but then a greater dream emerged. So I started writing the story of a woman in despair who goes to a psychologist who works with LOA principles but I came up against the fact that I can't describe things. I am not a literary genius and I don't notice detail. If you had lunch with me and somebody asked me what you were wearing during that lunch, I seriously wouldn't know because I didn't notice. So I couldn't write.
But when the idea came to write in the first person, as a love letter from the wife to her husband, I was up and running and the ideas came out of me in a rampage into a small recorder while I walked. The other thing that made it hard to be a writer is that I find it hard to sit still - not a good characteristic for a psychologist!
I didn't write because I was arrogant. I didn't write because it was easy. I wrote because I couldn't NOT write. I woke with the ideas in my head, I went to bed with more ideas in my head and kept the recorder by my bed. I wrote because, most of all, it was enormous fun. And as Abraham says, "If it's not fun, you're kinda missing the point."