My late brother was a psych major. I was reading one of his books once and I saw the regression lines for confidence and knowledge. it was very convincing. But then whenever someone tries to incite the effect this chart gets posted. I did not see this chart in my brother's book. I don't understand what it's supposed to show... Is it some kind of a distribution chart? I know that D&K asked people to fill in a questionnaire, they asked them "what do you think your score will be" and they answered 60. Then they linearly regressed (or whatever it's called) the best-fit line of what they thought they will get, with the score they got.

So that I understand. But what exactly is this chart? And where does it come from? I mean, what kind of chart it is? Because these should be two straight lines, not curves. Unless it's a distribution chart. Then, how is it possible to show the distribution of two things in one chart?

Thanks for your explanation. Here's the kind of chart that was in my brother's book. How did this turn into this?

https://www.janmagnus.nl/wips/dunning-kruger.pdf