This article by Dave West on InfoQ might be an interesting read if you’re interested in theories of software development.
“Both Lean and Agile must stop applying, in a literal and rote manner, the tools and practices. Tools and practices are nothing more than expressions of values, principles and philosophy. They are not the only possible expressions and may not even be the best expressions. Neither side will be able to realize their respective founders’ admonition to “use, adapt, and transcend” until and unless they come to understand why the practices and tools are what they are.”