There is a common misconception that the lines in the graph slope down, but they don't.
Kuaiyu
May 13, 2018, 7:20 p.m.
Actually their paper (and that graph) shows that people are just generally bad at estimating their skill levels (less skilled people will overestimate, but more skilled people will underestimate). Basically, everyone just stay between [50-80%] to adjust their estimation.