The title is actually what Dunning & Kruger found in their paper. Poor performers have no idea the difference between a poor performance and a good performance. If they knew how bad they were then they could tell the difference between good and bad. And of course, because of how quantiles work, there's going to be 50% of people in the bottom half.
(The classic usage of Dunning-Kruger effect to mean poor performers rate themselves higher than good performers isn't what the paper is about and you're welcome to read it [1])
The title is actually what Dunning & Kruger found in their paper. Poor performers have no idea the difference between a poor performance and a good performance. If they knew how bad they were then they could tell the difference between good and bad. And of course, because of how quantiles work, there's going to be 50% of people in the bottom half.
(The classic usage of Dunning-Kruger effect to mean poor performers rate themselves higher than good performers isn't what the paper is about and you're welcome to read it [1])
[1]: https://www.hep.ucl.ac.uk/~eo/stuff/unskilled%20and%20unawar...