Depends. There's a saying that 'the second draft is where you make it look like you knew what you were doing the whole time'. 'Discovery writing' is very common and many of the best authors - Niel Gaimen comes to mind - write that way. Maybe you just don't want to see how the sausage is made?

I will say based on my own experience writing a book: ideas you can understand without writing a book either don't warrant a book or probably have a perfectly good book written about them already.