There are Four core values for XP
The more you communicate, the less you make a mistake
The simpler the system is, the less you have to communicate
a. Feedback from tests
b. Feedback from people
The more feedback you have,the less risky it will be
It is the courage to make a overall change, or to throw away code.
And there is a deeper value: Respect between each other. "If members of a team don’t care about each other and what they are doing, XP is doomed."