[piva00]

It's a product of its time, it has seeded practices that for us is common knowledge nowadays. In 2005 it wasn't, most software companies were still stuck with long feedback loops, hierarchical decision making and goal-setting, over-analysis of requirements and little to no maneuvering room to change requirements once development was started.

It's vague exactly because it's a manifesto, not a handbook on how to apply it.