Promote yourself like mad if you want to be a published author. Even mediocre writers have got success in publishing by pressing their advertisement of their work. If you are phenomenal writer, but don't have any real contacts or publicity, your work will rarely get read.
Writers these days have to be half business and half pleasure. Although an agent and a publisher helps, it is good to know business and marketing so that you don't get cheated. You want to be able to understand what your contracts mean, and what your book marketing is all about. When you are writing, write for the enjoyment of it. But after the writing, you have to consider how to sell it. Art is enjoyment, but its result, to put it in the hands of public, is an entirely different realm that we should try to understand.