Doubt happens. It is part or the process. To proceed without having had doubts is foolhardy. To endure despite doubts is somewhat heroic (in that small personal sort of way).
The script can be a huge source of doubt. It sits there on the screen or on the page. You can spend countless hours studying it. And when you attempt to recall your original intent, you fear that those words were once carved in ice and now only vapor. But persistence in the face of such doubt is required.
Know that even the most braggadocios have doubt. Doubt is valid, but so is tenacity despite those doubts!
How do you manage your doubts? How do you overcome them?