If you do a good job of specifying a lean product, you might think you have your feature set under control. Most projects aren't that lucky. For many years, the holy grail of requirements management has been to collect a set of requirements—scrubbed, minimally specified, or otherwise—encase them in permafrost, and then build a complete product design, implementation, documentation, and quality assurance atop them. Unfortunately for developers and their ulcers, projects that have successfully frozen their requirements have proven to be almost as hard to find as the Holy Grail itself. A typical project experiences about a 25-percent change in requirements during development (Boehm 1981, Jones 1994).