A VERY SIMPLIFIED TUTORIAL (VERY SHORT) Correlation measures are misused in the presence of nonlinearities.
(How a measure of unintelligence can give the illusion of high correlation with performance.)
Correlation measures are not supposed to be used in the presence of nonlinearities. When 2 variables correlate half the time (in a symmetric way around the mean), correlation will not be 50% but will show ~90%. Part of debunking IQ studies. If IQ works for disabilities but does not correlate with success, there is an illusion of correlation because of the biases in the metric.