We will continually refine the design of the system, starting from a very simple beginning. We will remove any flexibility that doesn't prove useful.
In many ways, this is the most difficult chapter to write. The design strategy in XP is to always have the simplest design that runs the current test suite.
Now, that didn't hurt so bad. What's wrong with simplicity? What's wrong with test suites?
Let's take a step back and come on this answer a little at a time. All four values play into this strategy:
Communication—A complicated design is harder to communicate than a simple one. We should therefore create a design strategy that comes up with the simplest possible design, consistent ...