Abstract: Extremism is often made possible or fueled by group polarization: Like-minded people, engaged in discussions with one another, adopt a more extreme position in line with their prediscussion inclinations. Group polarization often promotes and influences norm entrepreneurs, who in turn help direct, unify, and energize those who listen to them, who in turn direct and energize norm enterpreneurs. The result can be a kind of spiral or tornado. Because of habituation, understood as diminishing sensitivity to stimuli, the energy provided by a transgressive or outre position is often less intense on Wednesday than it was on Monday, which means that norm entrepreneurs are often incentivized to up the ante. Spare as they are, these points suggest the importance of seeing extremism as a product of dynamic interactions among (1) group polarization; (2) norm entrepreneurship; and (3) habituation and thrill-seeking. These interactions might be formalized and subjected to empirical testing.