I'm translating a book, in which there is one sentence:
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Here is the cosmic joke:there is usually very little difference in talent between the person who earns $50,000 per year and the one who earns $100,000 per year. The only difference is that one has settled at a lower level while the other has refused to settle for less than $100,000.
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Here, what does "cosmic joke" mean?

I first thought it's a slip of the pen and should be taken as comic joke, or facetious remarks. But when I searched in Google the phrase "cosmic joke", it returned many results. So I think there might be such phrases.

Is there such a usage? And if yes, what does it mean?

Thanks very much.

Do inform me if you see any corrections needed in my written English.