Is something missing in the Agile Manifesto?

Brian Marick believes so. His post, "Six years later: What the Agile Manifesto left out" explores some missing values that aren't readily apparent by reading the Manifesto but are essential to have to be successful in Agile. Here's a summary of it (I've made bold the values that he believes is missing):

Now Agile is more respectable, a safer choice. The challenge isn’t so much getting a chance at Agile as it is executing once you’ve gotten the chance. There, the values of the Manifesto are not so helpful. Except for “individuals and interactions”, they face outward from the team. They don’t strongly apply to the relationships between team members, between the teams and their environments, and between the teams and their code. That’s a problem, because it seems to me that many new Agile teams are not executing. They’re floundering.

What should teams do with the time they’re not spending going too fast? They should invest in one of the four values I want to talk about: skill. Two skills that apply to pretty much any software project are refactoring and programmer testing (test-driven design). Those are skills that require a great deal of discipline. It’s awfully tempting not to write a test when it’s harder than writing the code, or to refactor some icky code you stumble on when that would mean blowing your estimate. Some of XP’s practices help with discipline. Pair programming turns what could be a solitary vice into a social act: you and your pair have to look at each other and acknowledge that you’re about to cheat. Peer pressure comes into play, as it does because of collective code ownership. Someone will notice the missing tests someday, and they might know it was your fault. Maybe the key driver of discipline is the practice of creating working software—running, tested features—at frequent intervals. If you’re doing that, you just don’t have time for sloppiness. You have to execute well.

I’ve observed that a characteristic of a good code base is that it’s habitable, that changes are comfortable, that the process of programming is one of ease. Agile teams suffer because they don’t think that wanting to make their lives easy is a relevant value, but it should be. There’s absolutely nothing wrong with finishing up a story by spending a half hour or so tinkering with code you’ve touched, just improving it—doing the software equivalent of hanging power within easy reach because the power strip on the desk is always annoying you.

I think Agile is suffering today because these fundamental values didn’t get written down and are too easily forgotten. As Agile moves into bigger companies and into less adventurous ones, those undocumented values are getting watered down. If that continues, I’m afraid Agile will be this decade’s fad that changes nothing. That would be sad.

Read more in his post.