It's actually a historically derivative joke. We're told that a non-Jew came to Shammai, requested that he be made a Jew, and demanded that he also be made Kohen Gadol. Shammai chased him off. The man went to Hillel and he accepted him as a student. Shammai went to Hillel and asked how he could possibly accept the man with the conditions he set, and Hillel explained that the man would begin at the very beginning of learning Torah, and as he went on he would develop understanding that G-d has set the conditions of the world and that one who is a convert simply cannot be Kohen Gadol by the nature of things.
|They're all in the same group, within a couple of years of|
each others' ages. But the smallest just can't reach what the
tallest can sometimes, and she's not going to win a race
against her. That's simple reality. They're still all great friends.
There were many possible good, holy reasons for the desire to be a Kohen: the opportunity to offer korbanos directly to G-d, to perform holy service, to lead the Jewish people. However, unlike among the other nations in which there were many temples and anyone could become servants or priests within those temples, G-d had directly designated the Kohanim as his priests and the Leviyim as their servants (Bamidbar Rabbah).
We do all have limitations. Some of us are only ever going to be so intelligent, intellectual, wealthy, handsome. We may never have the opportunity for the learning we want. We may not be the person we wish we were.
|He has significant disabilities. But he can cook|
great steak for dinner and hopes to become a
world famous chef someday with his own restaurant.
He accepts he has certain limitations but still has
plans to accomplish all that's within his possibilities.