When I was young, I just thought astronauts were lucky people who got to go to space. It wasn't until I got older and read through their bios (and such books as, The Right Stuff), that I realized they were actual uber-men/women...not only good at operating a space shuttle, but at a hundred other skills that may be needed when you're in space, including musical performances.
We are trained to be able to do everything onboard - we have to be. It takes many years.
To be an astronaut who orbits earth and stays for a while, it needs to become your main life's work. It takes: physical fitness to the highest standard, an advanced technical degree, and a proven ability to make good decisions when consequences matter. Then apply to the Space Agency of your country, and compete with the thousands who also want to fly in space.
One hell of an understatement: Hadfield was accepted as a trainee astronaut in 1992 and first flew in 2001. For the ISS alone, he got his slot in 2010 and trained until December 2012.
I met a backup astronaut (well, one who hadn't yet gone up to space) a few years ago...among her amazing engineering achievements, which I thought would've been enough for going into space, she was also a Division I NCAA track athlete.
The trials for Navy SEALS and other elite military ops are well-discussed...I wonder if NASA has any extreme tests they run...such as dropping off an astronaut on a remote island with nothing but flint and tinder and a shaving mirror and having to build a shelter with functioning refrigeration by the end of the week.
There's something along those lines in Rocket Girls, whose author generally plays close attention to realism. (No idea if that specific part is "true" though)
There was a recent car commercial, where they rapidly flashed scenes of the process of car design, with a voice-over reading "Bring out the designers. Bring out the mechanics. Bring out the nerds." Each sentence would show a stereotypical example of each. The designers were in a bright Apple-store-like office, wearing fashionable glasses. The mechanic was a long-haired guy holding a wrench.
And the nerds were astronauts, in launch suits, presumably walking towards a space launch.
It wasn't quite so idealist back in the shuttle days. Yeah, the pilot and commander and mission specialists were definitely amazingly qualified, but the payload specialists were pretty normal people.
