The impostor syndrome, sometimes called impostor phenomenon or fraud syndrome, is a psychological phenomenon in which people are unable to internalize their accomplishments. […]
Regardless of what level of success they may have achieved in their chosen field of work or study or what external proof they may have of their competence, those with the syndrome remain convinced internally they do not deserve the success they have achieved and are actually frauds. Proof of success is dismissed as luck, timing, or as a result of deceiving others into thinking they were more intelligent and competent than they believe themselves to be.
The Dunning–Kruger effect is a cognitive bias in which an unskilled person makes poor decisions and reaches erroneous conclusions, but their incompetence denies them the metacognitive ability to realize their mistakes. The unskilled therefore suffer from illusory superiority, rating their own ability as above average, much higher than it actually is, while the highly skilled underrate their abilities, suffering from illusory inferiority. This leads to the situation in which less competent people rate their own ability higher than more competent people. It also explains why actual competence may weaken self-confidence: because competent individuals falsely assume that others have an equivalent understanding. “Thus, the miscalibration of the incompetent stems from an error about the self, whereas the miscalibration of the highly competent stems from an error about others.”