I know of a writer that had an awesome idea for a great picture book. She had a daughter whose hair was always tangled and wanted to write a book about the tangle fairy. She put if off and years later, lo and behold, there her book was on the bookstore shelves - written by someone else! So, when the Muse strikes, listen!
If you can't put a padlock on your ideas, then how can you protect them? We all know that you can't copyright an idea, but if you fail to follow through with them, someone else may steal it from the Great Muse. And you'll come up a day late and a dollar short.
I think most writers do not willingly share their ideas with others for fear that someone will steal them. The best way to counteract this fear is to work on your favorite idea.
Sometimes when we get an idea that is so exciting, we want to tell people about it. I get enthusiastic and energized about the idea and have to share it with someone, even if that someone is one of my children. And sometimes, they get excited about it too and give me more ideas about what should be included in the book.
I always have several ideas that I'm working on at a time. And a list of more to work on as I finish the current ones. If you're able to work on more than one story at a time, make a list!
Make a list of five of your favorite book ideas and decide which one you will work on now. Follow through to the end so you won't face the same disappoint my friend faced. Write the story, and the query, and make your dreams of sharing the book with the world a reality. Now, go make that list. I don't want to hear you sighing, "If only I had written that book first. It was such a good idea."
Keep on keepin' on...