Why do astronauts exist?

Probes handle routine tasks better than people: they're cheaper, need no air, and can simply be lost. But they fail at the unexpected. When the Hubble Space Telescope ended up in orbit with a mis-polished mirror, a crew corrected the flaw with corrective optics installed on board; later servicing flights kept the instrument working. That same capability keeps the International Space Station alive: swapping pumps, hunting leaks, readjusting experiments. Sample collection works the same way: whoever is on the ground decides in seconds which rock is interesting.

The second reason is the human being itself. What weightlessness and radiation do to bones, muscles, eyes, the immune system, and the psyche can only be studied in crews, and without that data no flight to Mars would be responsible. That's why part of the research done on board is not aimed at space, but at Earth: bone loss, muscle atrophy, and fluid shifts happen in accelerated form in orbit, and there they become observable without anyone needing to be sick.

Historically, there was no research question at the start, but a race: when Yuri Gagarin orbited the Earth on April 12, 1961, the message mattered more than the experiment. National representation still carries weight today: astronauts are the showcase of their programs, and every new space nation sends its own people. Out of that, meanwhile, a pragmatic division of labor has emerged: robots fly where humans cannot survive, and humans go where judgment, manual skill, and the ability to improvise make the difference.