IT'S THE DREAM that most unpublished novelists share: selling your novel (finally), quitting your day job, and living the good life ever after.
So ... can you do that?
The answer is "Yes," but as you may imagine, there are a lot of conditions attached to it.
For instance, income from a novel tends to arrive in chunks widely separated on the calendar. If you are fortunate enough to sign with a publisher who pays advances (some do not), you'll typically get half of the advance upon signing a contract, and then the other half when the manuscript is agreed by all parties to be in final form (some publishers do this in thirds: a third on signing, a third on delivery and a third on acceptance). After that, if your novel earns out its advance (and the odds are against this with a first novel), it might be a year or more between your final advance check and your first royalty payment.
Even if your advance was lucrative enough to live on for a year or more, it takes tremendous financial self-control to make it with such sporadic income. It is not uncommon for first novelists to wind up in dire straits; in fact it is so common that I know of at least one publisher that requires first novelists to present proof of a second source of income as a condition of their contract.
There are things that will help. One is to sign a two-book contract and have both manuscripts ready at signing. This will increase what you have to work with, and probably space out the advance checks a little more.
Even better is to have three years' worth of income in the bank and ready to live on (separate from your 401k or retirement savings) before you sign that contract and deliver your two manuscripts. Saving up that sort of nest-egg takes time and discipline, but it does a tremendous job of helping to keep the wolf from your door.
Now, here's the funny thing; while I know some novelists who live entirely in the income from their book-length fiction, most do not. Some get a second income from teaching. Some work as freelance editors. Some (I'm one of them) hold down full-time nonfiction writing gigs; a measure that helps put important things such as health insurance on the table.
In fact, during the decade-and-a-half or so when I worked full time as a freelance writer, fiction was oftentimes the majority of my income, but it was never the entirety of it. Then, as now, I wrote travel stories, not only for the extra money, but for the fact that doing so allowed me to research the settings for my novels at no expense to me. And then, as now, I wrote speeches because (in addition to the extra income) doing so required me too write in another person's voice, which helped (and helps) to make my fiction sing.
Particularly in his later years, Mark Twain made most of his money on the lecture circuit. The poet Wallace Stevens never quit his job with an executive with the Hartford Accident and Indemnity Company. F. Scott Fitzgerald wrote for the movies. They knew what many novelists learn as they go along: that while it is possible to live exclusively on one's fiction, you just might find greater satisfaction if you make it part, and not all, of your professional life.