When is a Writer Good Enough?

Yesterday while making a pan of chicken parmigiana for dinner (homemade sauce, lots of garlic, fresh basil and freshly grated parmesan) I was listening to NPR and had the great fortune to hear this interview with Neil Gaiman. In talking about the inspiration for his new work The Graveyard Book, he said that when the idea for the book came to him and he actually sat down to write it, he came to the realization that "I am not yet a good enough writer for this idea. I am not yet a good enough writer to do this justice."

I've been thinking a lot about this comment. When is a writer not good enough? Do writer's return to their early work and think, "Yuck. This could be so much better."? I know when I write poetry I think that I'll never be very good, even with continued practice. Or do writer's complete a first work and think "I'll never write anything this good again."? ShelfTalker wrote a post a few weeks ago in which she asked "How often is an author's first novel their best?"

What's the point? I don't know. Someday I'll actually be able to take all these ideas swimming around in my brain and put them down on paper. Until then, I'll just keep wondering--when will I be a good enough writer to do this?