Nearly every good creative person I know has this awful feeling when first confronted by a problem that this time they won't be able to cope. I certainly do. Times without number I have smiled confidently at a client, promised I could handle the task - and gone away filled with despair, wondering if I was up to it. If you are not a writer or an art director, you may imagine that this feeling of panic is confined to 'uncreative' people like you. Well, now you know it isn't.
Big shots are only little shots who keep shooting.