Astronauts are the best of the best, not just overachievers who both reach for the stars and actually grab them, but also career students. They're constantly learning.
The time astronauts don't spend in physical training for the rigors of a space journey, they spend in classrooms, soaking up all the knowledge they can and learning about a wide variety of scientific areas so they can adequately perform all the experiments they'll need to do in microgravity, not to mention being aware of and knowing how to deal with a whole host of dangers.
You can believe that if an astronaut makes it to space, it's because they know their stuff.
But you have to think that they're a bit less used to dealing with ignorance on the internet.