But, I think the key realization is that whenever the incentives are strong enough, a lot of hard-working geniuses will be fighting for the prize. Hard-working geniuses are really hard to compete against, and if you don't realize that natural variation is a real thing, you can get discouraged pretty quickly.
Usually, those people are making disproportionate contributions to the world for comparably small rewards. Usually. We're lucky to have Einsteins and Bachs and Taos and an infinitude of less well-known but probably equally capable hard-working geniuses. I'm very grateful for hard-working geniuses who devote themselves to important problems! Some of them do apply themselves toward more secular ends, such as Gates. That's OK too, although the world takes care of gratefulness for me ;-)
It's just important to realize they exist if you ever get into a situation where you're regularly competing with them.
Google shows me nothing but out-of-context biology-textbook material, so I'll ask: what is the relevance here of "natural variation"?
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.