The term “meta-cognitive myopia” (MM) refers to the phenomenon that people are pretty accurate in processing even complex information, but they are uncritical and naïve regarding the history and validity of the source of the information received. This naive reliance on given evidence (hearsay, social media tweet, gossip, advertising, others’ opinions) is most conspicuous when the task context makes it crystal clear that the evidence is biased. Yet, judgments and decisions are nevertheless influenced by such invalid evidence. In this chapter, I illustrate MM in various paradigms: inability to ignore irrelevant information, change detection, conditional reasoning, judgment of causal power, and myopia for the impact of aggregation levels. MM offers alternative accounts of many anomalies and biases in judgment and decision-making, but also novel predictions of formerly unknown anomalies. A gullibility perspective on MM highlights the social responsibility to monitor and control rational behavior at the metacognitive level.