Imposter Phenomenon / Imposter Syndrome

An experience that occurs among individuals who are unable to internalize and accept their successes, instead attributing their accomplishments to luck rather than to ability. Individuals with imposter phenomenon are often fearful that others will eventually unmask them as frauds.

Reference:
Leary, M. R., Patton, K. M., Orlando, A. E., & Wagoner Funk, W. (2000). The Impostor Phenomenon: Self-Perceptions, Reflected Appraisals, and Interpersonal Strategies. Journal of Personality, 68(4), 725–756.