Do people advocate more on behalf of their own attitudes and opinions when they feel certain or uncertain? Although considerable past research suggests that people are more likely to advocate when they feel highly certain, there also is evidence for the opposite effect — that people sometimes advocate more when they experience a loss of certainty. The current research seeks to merge these insights. Specifically, we explore the possibility that the relationship between attitude certainty and attitudinal advocacy is curvilinear. Consistent with this hypothesis, we find evidence for a J-shaped curve: Advocacy intentions (and behavior) peak under high certainty, bottom out under moderate certainty, and show an uptick under low (relative to moderate) certainty. We document this relationship and investigate its potential mechanisms in three studies by examining advocacy intentions and the actual advocacy messages participants write when they feel high, moderate, or low certainty.