The Agile Manifesto is an immune response on the part of programmers to bad management. The document is an expression of trauma, and its intellectual descendants continue to carry this baggage.
Wow. Now that is an interesting perspective.
Conceptual friggin' integrity
The one idea from the 1970s most conspicuously absent from Agile discourse is conceptual integrity. This-another contribution from Brooks-is roughly the state of having a unified mental model of both the project and the user, shared among all members of the team. Conceptual integrity makes the product both easier to develop and easier to use, because this integrity is communicated to both the development team and the user, through the product.
I really like this. Conceptual integrity is such a great goal to strive for.
Behaviour has an advantage over features in that you can describe any feature in terms of behaviour, but you can't describe behaviour in terms of features. This is because features are visible while the software is sitting still, whereas behaviour is only visible while the software is running. Moreover, the presence of a feature can only indicate to a user if a goal is possible, behaviour will determine how painful it will be to achieve it.
This essay turns out to be infinitely quotable. All the more reason to read it in full! (via @beep)