Some writers won’t want to hear this, but writing more than one book really is essential if you want to succeed as an author. If you only ever plan to write one book, then you really are putting all your eggs in one literary basket, with a much lower chance of success.
No one cares about your book as much as you do. If you've written a book that you KNOW your readers will love and value, face the marketing paper tiger.
Yes, marketing IS a paper tiger. Being fearful of marketing is pointless. Just do it, and sooner or later you'll realize... "hey, this is fun!"
Just don't spend so much time marketing you don't have time to write. :-)