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An experience characterized by persistent feelings of inadequacy and incompetence despite one's training or accolades to the contrary. It is typically accompanied by the fear of being exposed as a fraud. The term is attributed to clinical psychologists Pauline R. Clance and Suzanne A. Imes. Despite the connotations of its name, "impostor syndrome" is not considered a mental illness. Despite having three degrees, I constantly worry that I will be exposed in the office as a fraud, so yeah, I guess you could say that I struggle with impostor syndrome.
See also: syndrome