Why do Islamist radicals engage in high-cost/risk activism that exposes them to arrest, repression, and even death? At a group level, it appears perfectly rational: zealous contention places enormous pressures on adversaries and in creases the likelihood that the group will achieve its objective. Robert Pape’s study of suicide terrorism provides some empirical evidence that extreme forms of activism do indeed produce concessions from opponents. Yet, although extreme tactics may be deployed as part of a logical, coherent, and rational strategy to maximize group goals, is it “rational” for the individual perpetrators? Why not free-ride off the efforts of others rather than jeopardize personal self-interest?