Hi. I'm attending a statistics course and there's a thing I can't understand. Using a dataset from Verbeek's book, I've found the regression linear model linking wage (as the dependent variable) and years of experience (the independent one) with Gretl. Then, our teacher told us to make the graphic analysis of residuals with respect to both variables (wage and experience). This is the residuals' plot:

The professor told us that this is a bad thing. But I don't understand why. It should be normal that higher wages show higher residuals. Could anyone help me? Thank you in advance!