When it comes to publishing in the modern age, I don’t think people care much about anything other than sales. As an author you can write something great, but if it doesn’t sell like hotcakes the miserable soulless scorekeepers in the publishing industry will say what the miserable soulless scorekeepers in every industry say: that you failed.
Because primacy of sales is not implicit in the word author, however, qualifiers become necessary. You can only be a successful author if you sell lots of books, or otherwise generate serious revenue in the form of t-shirt sales, film rights, speech-circuit fees, etc. It doesn’t matter if you generate all these sales by lying about yourself or duping your readers. The only thing that matters is the money.
If you write a book that is only read by world leaders, who take your words and change the planet with them, you will not be called successful. You might be described as influential, and the fact of your influence might drive future sales or offers to speak in front of go-go executives, but until the money rolls in you will never be described as a success. Not even if you save a million lives.
If you do not sell a lot of books but you receive critical acclaim then you can call yourself a critically-acclaimed author, or an award-winning author, but you cannot call yourself a successful author. Unless of course you were aiming for critical success all along, in which case you can pull a fast one and present yourself as a successful, critically-acclaimed author, thereby implying that you sold more books than you actually did.
If you are neither critically-acclaimed nor generating sales, then you can call yourself an author as long as you A) have written at least one book, and B) are working on another book, even if it’s only in your head. If you stop at any point, however, you become a failed author because you failed to achieve critical acclaim or financial success. In the writing business there is nothing worse than being a failed author. Except being a miserable soulless scorekeeper.
The antidote to all this, of course, is defining success for yourself. And I don’t mean that as a trite observation. Rather, I mean you should have an actual conversation with yourself about this issue and define why you’re writing and what it is you hope to give and gain by linking words together.
You don’t have to tell anyone what your definition is, and you can change it any time you want. What’s critical is simply that you know the answer yourself. Because if you don’t, the miserable soulless scorekeepers will gladly define success for you.