Almost nobody predicted the "Arab Spring." Immediately, however, scholars and other observers sought to domesticate this historical surprise by proposing causes that made the events seem, in retrospect, not quite so surprising. Scholars in social movement studies drew on that field's primary explanatory tools, including mechanisms from the dynamics of contention model that was introduced to the field in the early 2000s. Based on systematic comparison of 19 Arab-majority countries, this paper's research shows that this approach cannot clearly distinguish between the Arab countries that experienced widespread protest in 2011 and the Arab countries that did not. In theoretical terms, this study proposes that dynamics of contention in the Arab Spring cannot be captured by the anodyne concept of "mechanisms," with its mechanical implication that a particular set of inputs generates a particular sets of outcomes on a regular basis. This study presents case studies of micro-level dynamics during the Arab Spring that illustrate the varying ways in which particular mechanisms actually played out.