It happens so often as to be a cliche--the only "success" in this business is to do a good job on the last sentence you wrote.
It doesn't matter how many books you sell, how many copies are in print, how glowing your reviews are, how big of an advance you got. It still comes down to that silent battle with yourself. Last night, I basically went backwards, feeling stuck, erasing the two pages I'd fought through. I went to bed wondering if I'd ever be able to finish the book. Or if I was cooked as a writer. An almost unbearable sense of despair came over me.
My greatest career fear is that somebody's going to tap me on the shoulder and say, "Who do you think you're fooling?" Despite over 100,000 copies of my books in print, some awards, decent success in e-books, several projects in the works, and a revived career, I feel like I am getting away with something. "You mean I get to sit here and daydream, letting these make-believe people do whatever I want? And people will give me MONEY for it?"
But, since it's ephemeral, it can all go away in an eyeblink. And then it can seem like it never existed. I'm a Cancer, so I know it's just a feeling. The external reality is pretty much the same. A hard day of writing when I feel like a loser has the basic end result of a day when the keys are flying and the walls of the room fall away. Mashed all together, you'd never be able to pick the good days from the bad days.
As I dozed off, I thought, "Okay, I'm stuck, it's ruined already, so I may as well go to the most absurd extreme possible." Sleep on it. Get up and type before going to work. Walls fall away. I am in their world. Success. I can do this. Or, probably more accurately, it can create itself. Shut up and type.