Clarke's been very busy, he's published no less than seven chapters this month! Why is Clarke working so hard? Because he wants you to know that rolling rocks downhill is far easier than pushing them uphill.
In chapter 20 Steve discovers that software requirements are like forecasts. Forecasts - whether they be weather or sales forecasts - are invariably invariable (i.e. wrong). He learns about the shockingly high costs of building anything - be it cars or software - based on long distance forecasts. Waste, waste, waste.As have other Agile authors, for example: Mike Cohn and Jim Coplien, Ching is building his book iteratively in public view. So, after reading a chapter or two, you can offer him feedback and join discussions with other readers.
In chapter 21 Steve contemplates working iteratively from the start of the project - just like they do in product development. But he's got one great big niggling doubt ...
Clarke is also the author of the article: What Software Development Projects Can Learn from the Quality Revolution.