The book substitutes the core value of courage for the apparently 4th original core one of quality. The first core value is communication. I can't remember what the other 2 core values are, suggesting they are not core values, at least as far as I'm concerned.
I think the courage one is very interesting, because it is probably like laziness, impatience and hubris, something to be played with, rather than an ideal to be observed religiously.
'Discretion is the better part of valor', and Robert Nagler, the author, talks about how you have to play with the risks involved developing software, a very risky endeavor.
Perhaps communication is something that is a relative virtue too, ie something that you should or should not have to do all the time, the way it is in business negotiations. I wonder what those other 2 core virtues were.
He says: 'XP is the organizer in the Extreme Perl marriage that compliments Perl, the doer and fixer. XP's role is to keep Perl from fixing the car when the kids need to be put to bed'.
We can see who wears the pants in that marriage, which suggests why the book hasn't appeared on my perl radar screen before.
An interesting thing about XP he says is that the customer must speak with one voice, at the same time as he says that the customer may not know what it wants. Which seems to make impossible demands of the customer.
Despite that, it is the model of rationality and reflective action, when compared to education, where teachers are trying to develop learning in their customers' minds.
And despite that caveat about rationality, XP does seem a very dialectical approach. That is, it doesn't make sense by itself, but only as part of a thesis-antithesis-synthesis dance with the waterfall model, which is also a model of rationality and reflective action.