There are of course exceptions — but never, ever, never do this.
You can express doubt about the product, the market, even your pace of adoptions.
But never, ever let anyone see you don’t have 100% faith in getting the team through the journey.
They will never follow you, otherwise.
Doubts like these should only be shared with true co-founders, and maybe your #1 great advisor / mentor that you can really trust.