The term impostor phenomenon was introduced in 1978 in the article “The Impostor Phenomenon in High Achieving Women: Dynamics and Therapeutic Intervention” by Dr. Pauline Clance and Dr. Suzanne Imes. They defined it as an individual experience of self-perceived intellectual phoniness.
The researchers investigated the prevalence of this internal experience by interviewing a sample of 150 high-achieving women. All of the participants had been formally recognized for their professional excellence by colleagues, and had displayed academic achievement through degrees earned and standardized testing scores.
Despite the consistent evidence of external validation, these women lacked the internal acknowledgement of their accomplishments. The participants explained how their success was a result of luck, and others overestimating their intelligence and abilities.
Clance and Imes believed that this mental framework for impostor phenomenon developed from factors such as: gender stereotypes, early family dynamics, culture, and attribution style. They determined that the women who experienced impostor phenomenon showcased symptoms related to depression, anxiety, and low self-confidence.
You can see how shadow plays a part in this.