Agility and Feedback
For me the crucial difference differentiator of an Agile approach is the obsessive desire for feedback. Basically, if your reaction to an issue is to work out how you can get more, objective feedback faster then you are going towards the agile end of the spectrum; if it isn’t you are not.I will go out on a limb and suggest that the vast majority of system development failures are due to the lack of feedback at various phases of the development process.
This isn’t a new thought, it is as old as Kent Beck’s driving story from the earliest days of XP. It does get lost in all the talk of principles’ and ‘practices’ and ‘levels’ though.