It isn't working; you read it and reread it and your polished prose conjures magical images in your mind, but you know it doesn't fit even though you can't see why.
You begin to wonder if the problem isn't in the section you are working on, but in the setup somewhere else and you begin to ask yourself if there is a scene missing.
Wearily, you go back to the beginning and read through from the beginning. By the end, all you want to do is pat yourself on the back for being such a thoroughly decent chap.
And yet, the nagging doubt has not gone away and it won't go away. The flaw is hidden, buried under layers of polished prose, you feel it but cannot see it.
STAB IT!
STAB IT AGAIN!
DELETE EVERY THIRD SENTENCE, PASTE PURPLE PROSE AT RANDOM, COMMIT EVERY WRITER'S SIN IN THE BOOK!
STAB IT TILL IT'S MINCED THEN STAMP ON THE LITTLE PIECES UNTIL THEY ARE REALLY SORRY!