Even though the individual practices can be executed by blue-collar programmers, putting all the pieces together and keeping them together is hard. It is primarily emotions—especially fear—that make XP hard.
When people hear me talk about XP they say, "But you make it sound so simple." Well, that's because it is simple. It doesn't take a Ph.D. in computer science to contribute to an XP project (in fact, the Ph.D.'s sometimes have the most trouble).
XP is simple in its details, but it is hard to execute.
Let's run that again. XP is simple, but it isn't easy? Exactly. The practices that make up XP can be learned by anyone who has convinced someone else to pay them to program. That isn't the hard part. The hard part ...