Plans make us feel safe. And even if they're useful, we'll reach success by getting out of our comfort zone.
Obvious value is obvious: working software over comprehensive documentation
Product Design is an engineering process. It is not just about drawing a beautiful user interface, it is about building a solution to a user's need. It is a succession of logical steps in thinking and writing, which I recommend to browse through sequentially. And the best approach to my experience is going top down.
An invention may not sell itself. Even a genius and visionary person may need to lean back, go through the basics and eat his own dog food before he can actually make money out of it.