Much social movement research concerns processes of mobilization; understandably, because mobilization is the mechanism that brings demand and supply of protest together. Without mobilization there will be no action even in circumstances of high demand. The study of mobilization concerns such matters as the effectiveness of persuasive communication, the mobilization channels employed, the influence of social networks, and the perceived costs and benefits of participation. As for the effectiveness of communication, organizers must solve a crucial problem, namely, which are the people in demand of protest and how can they be reached. Sometimes this problem is easy to solve, if for example, it regards the inhabitants of a neighborhood or the workers in a company, but often there are no such easy solutions. Under stark repression mobilization is extremely difficult and indeed dangerous. Censorship makes newspapers, radio, and television unusable, while organizers and movement activists run the risk of being imprisoned or worse. Oppressive societies offer examples of people high on demand but low on supply of protest and failing mobilization. Once protest movements come out into the open and mobilization can no longer be oppressed, the system quickly collapses.