There is no shortage of stories on attempts to adopt methods requiring significant discipline and effort, only to find compliance drop off dramatically shortly after its introduction. The psychological and social factors necessary for sustained adoption are missing. The agile methodologist Alistair Cockburn asks people and teams, "Would you do these practices again?" This is arguably a more important question than the inherent value of the practice.
The creators of a few agile methods (e.g., XP and Crystal) recognized that human factors such as enjoyment, simplicity, short-term reward, peer pressure, and lots of gain for the pain are important ingredients to create fertile soil for sustainable self-discipline with practices. Not surprisingly, XP practices rate well in response to Cockburn's question [Cockburn02].
For example, test-driven development reveals its payoff quickly to those who try it; developers enjoy the small win of making a test pass and the design clarification that comes from writing the tests before writing the code to be tested.