Consensus

A team of developers can be effective for the long term to the degree that they can make the good decisions regarding code cleanliness that extreme programming reserves for them. S2

Individual experience varies widely even among skilled developers. Only shared experience in a particular codebase will lead to consensus. Reading each other's code helps but cannot duplicate that of programming together while discussing the present and future impact of every decision made. S9

Test-driven development enables pair-programming by sequencing new experience based more on recent experience than on deep personal experience unavailable to a companion. S10