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Dunning, D., Johnson, K., Ehrlinger, J., & Kruger, J. (2003). Why people fail to recognize their own incompetence. Current Directions in Psychological Science, 12, 83–87.
It does appear that top performers tend to be a bit modest while bottom performers greatly exaggerate their abilities. Dunning et al. call it a "double curse" - those who do not have the knowledge or skills are likewise those who cannot gauge their own knowledge or skills.