1. You are a traditionalist. Writing is your life and you cannot be bothered with all the minutia of bringing your work to the public. THAT is why there are publishing houses out there!
2. You don’t have the graphic skills necessary to create a finished marketable product from your story or know how to find those that can help make your book real.
3. You don’t have the time, you want to write and only write. And you know that if Dan Brown can be published you have a very good chance of getting your stuff into Barnes & Noble too.
4. You are not organized. As you write you can’t envision what your book will look like in its final form.
5. You have a relative working for one of the big five publishing houses who actually thinks your work is good enough to champion the piece before the editors (his bosses).
6. You are broke, living in a French garret two blocks from the Moulin Rouge. The rent and the cold are killing you but the words just flow, that’s what your role model Hemingway did and look what he became.
7. You are not a fan of Facebook, Twitter, LinkedIn, Pinterest, etc. You think they are mind and time sucking holes in the universe and you are better than all that.
8. It will cut into your drinking and alone time. You need to puzzle out the next complication of your story, not try and find an ISBN number.
9. Your unemployment checks will soon stop (a conscience decision to leave that crap job and make a name for yourself like John Grisham) and you just know that the next rejection slip will not be a rejection slip but a contract. No one in their right mind can pass up your manuscript and you mention that twice (for emphasis) in your cover letter.
10. Your mother told you again they will be remodeling the basement and your desk and cot are not included in their plans. You remember fondly the two weeks you spent riding BART trains through SF Bay Area scribbling in your Safeway notebooks dreaming of that Scribner contract just before she told you that you could move back into the basement the first time.
There are many options that help you bring your book to life, from traditional publishing and agents to self-publishing and the many levels between. It has always been my take that each has its value and purpose depending on the writer and the story. Neither is necessarily better than the other but going traditional is a lot more frustrating. Self-publishing can potentially and personally cost more since you have to cover all the costs for editors, book designers/builders, cover designers, even shipping and marketing. But you are in control, you make the decisions, and you willingly can live with the results. And remember, most importantly, you also own the whole product.