That's the no-fun advice from the Dystel & Goderich Literary Management blog:

So what's a first-time author to do? My advice is to keep the day job--the benefits are more than financial. Let's go back to the writer sitting at home. Publishing is not glamorous; it's hard work. The full-time writers I know work harder and longer than their peers. They spend much more than eight hours a day writing, thinking about their writing, wondering what their agent is thinking, pondering the loss of yet another editor, desperately trying to refrain from e-mailing their publicist again about that review in the Sioux City Herald, talking with other writers (about their agent, editor, and publicist), blogging, and generally praying that they won't have a coronary before the end of the day. Authors who have day jobs are often able to put things in perspective: there's more to life than their book(s). They get to leave a large part of the worrying to us agents (it's part of what we're paid to do), and that's as it should be.

I will say this: when you're working from home, how often can you hope for the windfall scraps from the important lunch meeting you weren't invited to?