Oddly enough, however, it makes too much sense. If these conditions are all that is needed for the mafia to originate, why then is the mafia not present wherever there is a thriving economy? If urban-coastal markets so fostered the growth of the Sicilian mafia, why did it not flourish in other urban areas of southern Italy? Why, for instance, does the tradition not exist in towns such as Messina and Siracusa—or for that matter towns throughout southern Europe—which are not ostensibly more impoverished? Conversely, if the profits provided by a bustling economy are an essential prerequisite, how could the mafia have emerged in the poorer towns of the interior such as Caltanisetta and Agrigento

QUESTION: What additional factors distinguish the mafia's birthplace from otherwise similar coastal and interior towns? The argument points to a missing explanatory variable.

Diego Gambetta, The Sicilian Mafia The Busi…, loc. 223