The dominant political science explanations of the causes of individual-level political participation converge on three sets of antecedents—resources/skills, recruitment, and political engagement. However, the overwhelming majority of the empirical tests of these antecedents rely on cross-sectional data, obscuring the fact that micro-level participation in the United States is more accurately characterized by instability rather than by stability. Using the American National Election Study and Jennings time-series data, we for the first time demonstrate the inability of traditionally examined antecedents to explain individual-level variation in political behavior over time. Finding extant theory inadequate in this regard, we propose a modification of participation theories that puts the concept of motivation in the foreground. We argue that a model that includes motivation may both pave the way for a better understanding of the variation in participation over time and suggest possible prescriptions to help alleviate representational biases at the individual level.