You will likely spend more time promoting than writing. A good book is no guarantee of success. Imagine the futility of serving an exquisite dinner at an empty table and hoping to be named an award-winning chef. Who will know if you don't tell them? Writing the book is only a tiny part of the work that goes into making it successful.
Nataly Kelly has some interesting insights about publishing her book.
She actually made contact with a Penguin editor via social media. Who knew?