There are a number of examples of people bold enough and entrepreneurial enough to create and publish their own books, often leading to being traditionally published and marketed.
Christopher Paolini began writing “Eragon” at the age of 15 and his parents decided to self-publish the novel, which was re-published by Alfred A. Knopf.
“The Artist’s Way” began as a collection of “tips and hints from different artists and authors” by Julia Cameron and Mark Bryan. After it was turned down by literary agency William Morris, they self-published it and it was later published by Jeremy Tarcher (Penguin) in 1992.
The book was eventually put into the “Self-Publishing Hall of Fame” after “selling millions of copies worldwide.” [Wikipedia]
Author and personal development coach Tama Kieves self-published her first book “This Time I Dance!: Creating the Work You Love” and its level of popularity led to Tarcher/Penguin re-publishing new editions.