Isn’t part of this related to the fact that there’s always more room for improvement at the bottom?
Yes. Imagine a baseball player who is 5 for 15 and another is 0 for 15. The first is batting .333 and the second .000. Now they each go 5 for 5. The first guy is 10 for 20 or .500. The second guy is now 5 for 20 or .250.
The first guy's average went up .167 and the second guy's went up .250.
Hey, that's not FAIR!
Of course it is harder to improve when you are near the top of your class. Imagine a kid whose average is 99% and other whose average is 50%. Let's say each wants to improve his average by 2%. In the absence of 'extra credit,' it is impossible for the 99% kid to go to 101% but it is possible for the 50% kid to go to 52%.
Hey, that's not FAIR!