The Illusion of Explanatory Depth (IOED) occurs when people overestimate their ability to explain the causal mechanisms of natural or social processes. Prior research has attributed this metacognitive bias to confounding the understanding of abstract causal patterns with the comprehension of domain-specific mechanisms. However, this explanation does not account for the differences in the magnitude of IOED among topics with similar causal properties or belonging to the same explanatory domain. In four experiments, we investigated whether the social desirability of knowledge about historical events and legislative proposals influences the estimation of their causal understanding (Experiments 1, 2, and 3), and whether this effect is moderated by the ability to perform controlled processing (Experiment 4). The results showed that the IOED was higher in topics whose knowledge was rated as more socially desirable (Experiment 1) and that this effect was not due to lack of familiarity or to self-enhancement bias (Experiments 2 and 3). Additionally, the ability to carry out Type-2 processing was associated with a reduction in the effect of social desirability on the IOED (Experiment 4). These findings demonstrate the importance of developing models that integrate dual processing theories in the understanding of metacognitive processes.