Are overconfident beliefs driven by the motivation to view oneself positively? We test the relationship between motivation and overconfidence using two distinct, but often conflated, measures: better-than-average (BTA) beliefs and overplacement. Our results suggest that motivation can indeed affect overconfidence, but only under limited conditions. We find that motivation does indeed inflate BTA beliefs. However, introducing some specificity and clarity to the standards of assessment (Experiment 1) or to the trait’s definition (Experiments 2 and 3) reduces or eliminates this bias in judgment. We find stronger support for a cognitive explanation for overconfidence, which emphasizes the effect of task difficulty. The difficulty of possessing a desirable trait (Experiment 4) or succeeding on math and logic problems (Experiment 5) affected overconfidence in ways that are consistent with the cognitive account proposed by prior research, above and beyond motivation. Finally, we find the lack of an objective standard for vague traits allows people to create idiosyncratic definitions and view themselves as better than others in their own unique ways (Experiment 6). Overall, the results suggest motivation’s effect on overconfidence is driven more by idiosyncratic construals of assessment than by self-enhancing delusion. They also suggest that by focusing on vague measures (BTA rather than overplacement measures) and vague traits, prior research may have exaggerated the role of motivation in overconfidence.