I think that sentence is meant to highlight one weakness of that measure. It may be a good heuristic in many circumstances, but if you have direct knowledge abo

I think that sentence is meant to highlight one weakness of that measure. It may be a good heuristic in many circumstances, but if you have direct knowledge about the problem domain (like in the football players example), applying this specific heuristic may give better results than using the generic one. To solve difficult problems with approximate methods, you usually need to combine several heuristics anyway.