Of all the constants in the universe, two seem to be unique to the book industry: the prevalent belief that everyone has at least one good book in them, and the romantic belief that the author's role after publication is to sit back and collect checks. These beliefs might have been based on truth more than a hundred years ago (if then), but they certainly are not true today. In an industry that publishes more than 400,000 titles in the U.S. each year, authors who don't understand the book industry and are unwilling to work toward the success of their book will find themselves unpublished—or worse, self-published with $10,000 worth of books and no one to buy them.
The problem, of course, is competition. A century ago the cost and difficulty of printing a book was great enough to limit competition. Authors could only be published if they found a publisher willing to invest in their manuscript. As a result, only the best books were published. Consumer confidence in books was very high due to high product quality, and as a result, authors were not regularly expected to promote their books.
Fast-forward to the present where printing technology is cheap and the Internet enables world-wide availability. On the surface, this combination would seem to allow myriads of authors who have at least one good book in them to put that book in front of the masses and reap the rewards of authorship. In truth, it has fostered an explosion of new books, but that explosion has not been (and cannot be) accompanied by an equivalent explosion in retail shelf space. Browsing the shelves of Amazon.com is not at all like browsing the shelves of your local Barnes & Noble bookstore. Books do not sell simply because they exist. The public must know about them, and in some way be convinced to buy them. With so many options to choose from, the public is becoming less inclined to search for a good book. Instead, they want good books presented to them. And the authors and publishers who do this best will sell the most books.