Giff Constable makes the case for validation and learning in the product development process before you launch something. From You Are Spending 3x-5x More Than You Should:

Agile/lean has helped people debunk the “big upfront design” phase, but far too many replace it with nothing. I agree that waterfall-style, big-upfront-design is a waste of time and money. I do believe that getting into the market with a designer and an engineer and learning is a critical use of time.