I think a lot of people think of "work harder" as "work harder to better yourself" (like learning new skills or becoming better at things you already know), not

I think a lot of people think of "work harder" as "work harder to better yourself" (like learning new skills or becoming better at things you already know), not just "put in the hours and try really hard and do your best". If you use the former definition instead of the latter (which is the way I think a lot of people use the term), there is probably a lot more of a link between working harder and making more money. I'm just guessing though. I have no data to back it up.