There is nothing so devastating as being scared to write down the thing which is on your own head. Such a paradox to create something and then not bring it to the light of paper or screen.
There is nothing so devastating as to want to create, only to fear the outcome.
Sometimes dear ones, these things happen. Especially, when it something outside of your normal comfort zone. Something that may be seen as a little wilder. Sexier. Scarier. Darker.
The doubt is most disconcerting, yes. But, it is not insurmountable. Consider it the reminder of your mortality. The reminder that every story, every idea, has and needs a certain amount of care. A level of respect and concern before beginning and finishing any work.
It could even be a guard to being to hasty before starting a new work. Switching a genre. Even thinking of using a pen name. Sometimes the doubt can allow the story to incubate, stew a while. This way when you come back it, the thought–your thought, subject to your talent and its skill–is or may be more easily managed.
The doubt is a yellow light, a stop sign. But it is not, nor should be a considered a brick wall. Listen to the doubt. Sometimes its background noise, sometimes it it’s your imagination reminding you to just wait a minute. In the waiting, you may just make what would be a good story into something phenomenal.