If you are able to deliver a better result than "Person X" who is paid more than you, and if you get a chance to deliver that result, won't you demand to be paid more than the "Person X"?

And for the company who is paying, who already seems to agree to pay that much for "Person X"'s result - would likely to be happy to pay you the same or more since you are delivering more

Where am I wrong? Isn't this just capitalism? Help me understand :)

If you voluntarily say I need only half the pay of "Person X" aren't you basically being charitable or just sacrificing what you could potentially get? I am not saying that doing this is wrong (probably morally right) but this is probably rare.