Work hard and you will be rewarded. It sounds simple. But remember what it was like studying for a test? Some kids studied forever and did poorly. Some studied hardly at all and made great grades.
You can spend incredible effort inefficiently and gain nothing. Or, you can spend modest efforts efficiently and be rewarded. The purpose of what you do is to make progress, not just to expend yourself.
Effort is the single most overrated trait in producing success. People rank it as the best predictor of success when in reality it is one of the least significant factors. Effort, by itself, is a terrible predictor of outcomes because inefficient effort is a tremendous source of discouragement, leaving people to conclude that they can never succeed since even expending maximum effort has not produced results.