One of the most widely used agile methods is Extreme Programming (XP) which include the practice of pair programming. The goal of XP is to share experiences and qualifications in order to raise the quality of the produced code. Among others this can be done using the synergistic benefits of refactoring, simplicity and pair programming. Our claim in this article is that the Achilles heel of XP is pair programming.<br/> In this article we raise serious concerns regarding the dominating role pair programming has in XP as it influences a range of the other practices including refactoring and simplicity. This could have the undesirable side effect of a negative influence on the synergistic effect.<br/> Using action research as the research mechanism, we show that simply setting two people together to work, does not necessarily have a beneficial result for XP.<br/> We conclude that it can be reasonable to consider team building as a resource to enhance the chance of achieving a positive outcome of pair programming.