If you've never been published before, you're an 'unknown quantity', so you're going to have difficulty selling your first novel.
('chiefly US') The 'big unknown' [=the important thing that everyone would like to know] is how investors will react.
A 'fear of the unknown' kept her from changing jobs.
(..) So what'd they say? He's fixated on the missiles. But the codes are constantly being changed. By whom? Parties unknown. We have an ally? Ultron's got an enemy. That's not the same thing. Still, I'd pay folding money to know who it is. I might need to visit Oslo. Find our "unknown." (..)2015 Avengers: Age of Ultron