This article explores why people adopt different processes to participate in mass mobilizations, using the 2006 Anti-CPE (labor law) Movement in France and the 2008 Candlelight Movement against American Beef Imports in South Korea as case studies. In France, initiators and participants followed the ‘ready-made’ way: left-wing organizations led the whole process of mass mobilizations. In contrast, in South Korea, initiators came from ‘nowhere’: they were middle and high school students without any political organizations; participants were ‘tainted’ by the left-wing political line. The key finding of this study is that the levels of demarcation of political lines in people’s everyday life may explain this difference. In France, strong establishment of a political line in people’s everyday life brought fewer new actors, creating less surprise but a solid mobilization; in South Koreas, the less-established political line in people’s everyday life attracted more new actors, creating more surprise but ‘frivolous’ mobilizations.