Some people have better luck with doubt than others.
Some people establish rituals to offset doubt: rituals that become steadily more complex and harsh. “Oh, I can’t write unless I have my favorite notebook and tea and absolute silence!”
Some people freeze. “I cannot. I cannot. I must not.”
Some people become giddy.
Some people put on blinders and stick to the plan.
Some people forget the plan, forget everything, cannot make decisions, feel lost and panicked and afraid of everything as it becomes overbright and garish, like being surrounded by monstrous clowns.
Some people are stubborn and blame writer’s block or say they don’t have enough time, or say or think anything that lets the doubt slide by without having to feel it.
But the doubt must be there; otherwise, your characters won’t feel the possibility that happily ever after might be forever out of grasp, or, (if you’re that kind of writer) that the possibility that happily ever after might be within their grasp (oh horrors).
The writing of every story that rises and falls must be afflicted with the passion of doubt, or else the readers will never doubt either.
And no mistake: doubt can be a passion.
Sometimes we control our passions with rituals. And sometimes with panic. And sometimes with excessive twitchiness, or even with horror. But mostly by denying it. But a denied passion never disappears; passions must be acknowledged and honored, if not precisely obeyed.
What kind of story is it, without doubt? –A clockwork story.
The doubt is part of your function as a writer: without doubt, you are no writer, only a hack or a zealot. There must come a place where the formula is destroyed, all sense is lost, and the path is occluded for not having been yet created, no matter how clear it seems when you look back later.
There is no answer of how to face the doubt.
If you face it: you’re a writer.
If you face it, when you face it. Years may pass, no blame. The terror of an instant is no less fiercely felt.
No one can go into the room with the doubt but you; no one can face it but you; no one can answer the riddle of it but you; the answer that you gave last time won’t suffice, no matter how many times you’ve done this before, no matter how many rituals you perform or don’t perform.