Ontological security theory posits that states seek to provide their citizens not just physical but also cognitive security, mostly through routinised foreign policy practices that reinforce notions of the national Self. Several studies established this theoretical assertion at the individual level, using various qualitative methods. This study adds to the literature by taking an experimental approach to provide further empirical support. It develops a novel index for the measurement of foreign policy behaviour’s effect on individual citizens’ ontological security and employs it in a survey experiment. The experiment examines whether Jewish-Israelis experience change in their sense of ontological security due to their state’s deviation from its long-standing offensive–defensive security doctrine. The findings demonstrate that citizens indeed form an attachment to their state’s foreign policy practices and that deviation from them can impair their sense of ontological security. This suggests that seemingly rational, strategically warranted policies might sometimes bear unexpected costs for policymakers.