Good question...And one I would have answered exactly the same as author J. S. Wayne, even before I knew of him, in an article he wrote for Wordpreneur:

One or One Hundred Million?

So you’ve finally published your first book. Whether it was self-published or you went the more traditional route, you’ve got that first, shiny-covered book in your hand. Now you can give a wave to the people who supported you. You can also do the same to the people who said, "So, when’s that book coming out again?" only with less fingers, if you’re so inclined.

Then, you sell one. Or two. Or two million. And you ask yourself, "At what point do I start working on the next one? How many fans do I need to make it worthwhile?"

The answer is the same as: "How many copies do I have to sell to be able to put ‘published, SOLD author’ on my resume?"

One.

That’s all it takes to be a published, sold author. And that’s all it should take for a writer to say, "I’m going to finish what I started."

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