As the Arab Spring’s second ongoing wave shows, innumerable activists across the Middle East continue to mobilize for change. Yet mass mobilization has not always generated a mass movement – that is, an organized collective actor with defined leadership, a cohesive identity, routinized coordination, and indigenous structures of survival. In Morocco, Jordan, and Iraq, multitudes of spontaneous and overlapping protests struggled to engender a durable coalition and national movement. Activists partly formalized their strategies through movement-building in Lebanon and Algeria; but only in Sudan did a cross-cutting movement and coalitional leadership representing popular demands fully crystallize. Why this disconnect between youth-led mobilization and movement-building? Traditional answers from contentious politics theorizing, such as repression and opportunity structures, mistakenly assume that mass movements logically emerge once activists surpass a critical threshold of resistance. Critical work by Schwedler and others rightfully highlight how protest events operate with their own strategic dynamic at the micro-level, but this also leaves untouched the wider explanatory question of why only some protest events result in movement formation. This paper fills this gap with an innovative answer gleaned from theoretical synthesis and comparative analysis of three representative cases (Jordan, Lebanon, Sudan). Insights from fieldwork, including immersion in youth activist networks, combined with multilingual documentary evidence, suggest that three conditions explain the puzzle of mobilization without movement: 1) geopolitical interference, 2) civic density, and 3) cognitive heuristics. The more that are present, the less likely coherent movements can coalesce. First, international support enables embattled regimes to disrupt or repress uprisings in local settings before they spread or adapt across national spaces. That Sudan was the most geopolitically isolated country is no coincidence, as its rulers had least access to Western and Gulf reservoirs of economic and military assistance. Second, at the institutional level, when civil society groups are not only unified but imbricate themselves into youth-led protests early on, the roots of robust coalitions are laid down. For historical reasons, however, some Arab civil societies tend to feature highly fragmented and or compartmentalized institutions, leaving protest entrepreneurs in a precarious position. Finally, activist vanguards must overcome cognitive biases related to availability and recency, both of which overemphasize the success of horizontal, informal, and leaderless insurrections in toppling dictatorships during 2011-12. That strategy traded durability for agility, privileging spontaneity over long-term organization. Adapting towards movement-building thus may require “unlearning” this particular lesson from the Arab Spring.