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 these faces of overconfidence, but only under limited conditions. Whereas BTA beliefs are inflated by motivation, 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 overall. 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 self-assessment more consistently than does 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 BTA beliefs 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) and vague traits, prior research may have exaggerated the role of motivation in overconfidence.