Your use of Dunning-Kruger isn't quite accurate. The better you are the less likely you are to overestimate yourself, unless you are in the very top, in which case you are likely to underestimate yourself in relation to others. Basically, because people have relatively little interaction with people that are very different from themselves, most people tend to rank themselves in the 3rd quartile, whether they are from the bottom two or from the top. That is very different from not knowing what you are capable of.