Past findings indicate that middle-aged adults in the United States tend to be more resistant to attitude change than younger and older adults, but little is known about why this is so. The authors propose that midlife adults' disproportionate occupation of high-power social roles (which call for resoluteness) may partly explain their heightened resistance to persuasion. Using nationally representative data sets, the article first documents that in various domains the possession of social power peaks in midlife. It next documents that middle-aged adults place a high value on resoluteness, which suggests that they have internalized powerful role norms. Next, it shows that directly activating the concept of social power increases the perceived value of resoluteness. Finally, it demonstrates that the possession of powerful social roles partially mediates the relationship between age and resistance to persuasion. This work is the first to uncover a mechanism responsible for changes in attitude strength over the adult life course.