They are selected for being remarkable in one way or another, then trained in extraordinary disciplines.
Then they visit space, and the experience - including the Overview Effect - alloys them, fixing that extraordinariness in them.
All of them that I have met possess a solidity, as if they are more dense or more real in consequence than everyone else.
I have the reaction that if I've chosen not to be an astronaut, I better find a very good path to extraordinariness of my own.
Put simply, they are Persons of Consequence: the positive aglaec-ness is obvious in them, and we are challenged to find our own.