Why do some Islamists pick up arms as opposed to others who live under the same conditions? Environmental explanations such as culture, occupation, or poverty cannot differentiate between the two groups. Instead, I draw on the belief system literature and use a cognitive mapping methodology to compare Islamists from the nonviolent Muslim Brotherhood and from the formerly violent groups al Jihad and al Jamaa al Islamiyya in Egypt. To ensure that my findings are not specific to individuals who believe in Islam and live in authoritarian countries, I also examine violent and nonviolent non-Muslims from a different environment - members of the Baader-Meinhof group who attacked the German state during the 1970s and German political activists who at the same time decided to not pick up arms. Data were gathered from in-depth interviews in Egypt and Germany. I identify eight different kinds of decisions to pick up arms and make two main claims. First, there are at least three chains of reasoning without which decisions to pick up arms are not possible. These chains refer to 1) attacks observed by the individuals, 2) perceptions of their local political structures, and 3) their private and political activities. Second, decisions to use or not use violence must contain combinations of components from different chains. These combinations create both the possibility to take revenge and to identify a target; and exclude alternative means and goals. The paper concludes with an exploration of the action implications of counterfactual initial conditions and the possibilities of nonviolent Islamists "becoming" violent and vice-versa.