I just meant "some people are smarter/more productive than others for reasons beyond either person's control at the time of measurement".

So it could be environmental factors (access to better support or higher quality educational experiences in early childhood). Or just genetic. I'm not positing any specific causes, just making a general observation that I find to be true of the world I see around me: especially at the highest levels, some people really are just smarter than others, and no amount of hard work could close the gap.