If you're an entrepreneur or are thinking about starting a company, Steve Blank's blog is must-read material.
Steve's latest series of posts establishes the reasons why Customer Development and Lean Startup methodologies are so important (and why prior models of startup development often resulted in failure). Read them in order:
The Leading Cause of Startup Death
Customer Development Manifesto Part I
Customer Development Manifesto Part II
Customer Development Manifesto Part III
Customer Development Manifesto Part IV