Why do I recommend you keep quiet about your new book idea until it's developed?
Self-doubt. Your story idea is in its fledgling stage. You haven’t worked out all the plot details, your feelings see-sawing between whether this new project is awesome or awful. You’re on the brink of committing your time and energy, but that niggling self-doubt is whispering in your ear about perhaps instead of this story idea you should be choosing another. And guess what happens when you switch to a different idea? Another plot idea appears as the better choice. Before long you have several false starts with no progress.
A less than enthusiastic response from a relative/friend/author/babysitter/mailman could kill your idea before you’ve even written the first chapter. The critique stage comes much later when you have a written draft. Even then, be careful who you share your manuscript with. Use qualified critique partners familiar with your genre.
Also, instead of talking endlessly to others about your unwritten book idea – write it!
At writers’ groups I’ve meet too many writers still talking about their idea; procrastinating week after week, month after month, and some year after year, without actually writing their story.
So, in the early stages, when someone asks you what you are currently working on I suggest you give a vague answer – “A children’s/romance/horror/mystery novel, but it’s still in the development stage. “
If they get persistent just give them your author business card/website address and tell them they can follow your progress online. Or even better, ask them to sign up to your online newsletter (collect their email address), and they will receive your author updates.
Best wishes with your writng journey,