I think you are referring to the Dunning-Kruger Effect. It describes the relationship between experience one has in a particular topic and his/her confidence about being an expert.
Dunning and Kruger argue that when people know nothing, they also know that they know nothing. However, after learning only a little bit, people seem to be very confident that they understand everything of the subject.
With more studying, one realizes that there is more to it and might feel insecure even. However, after studying more and more and more and people become an expert, people begin to realize that they do know a lot, but that it is impossible to understand everything.
Both the x- and y-axis have no scales because the Dunning-Kruger effect is only conceptual. The following image, does nicely present the train of thoughts through the graph:
Kruger, J., & Dunning, D. (1999). Unskilled and unaware of it: how difficulties in recognizing one's own incompetence lead to inflated self-assessments. Journal of personality and social psychology, 77(6), 1121.
Pictures taken from: https://www.linkedin.com/pulse/dunning-kruger-effect-confidence-vs-over-confidence-harshil-rastogi