My uncle was a radiation oncologist who worked with machines like this one. As a young child in the early 90s he took me to the hospital where he worked to watch him and their staff physicist calibrate a linear accelerator - an experience I remember vividly. A very long checklist culminated in them irradiating a plate of acrylic, which I got to keep. The plate was about 20cm x 30cm x 4cm and aligned such that the beam would strike the 4cm face and travel down the 20cm side, fanning out in the process. The result looked like a thinner version of this: https://en.wikipedia.org/wiki/Lichtenberg_figure#/media/File...

I asked him how they could possibly use such machines on humans, given what I just watched it do to a 1kg plate of acrylic. He told me that they hit the plate with way more energy than they ever would a human. That prompted my followup question: "uncle, what happens if you accidentally hit the wrong button?" He told me that accidents like that used to happen, but that the machines they used had special computers to keep the patient safe even if he made a mistake. "But uncle, what happens if the computer makes a mistake!?" I had no idea what a bug, or for that matter code was. He didn't have a good answer beyond "the computer can't make mistakes like we do." Having played with computers enough by then to know that his statement wasn't entirely true, I ended that outing wanting to know more. I started obsessing over what would happen to people if computers controlling things like that linear accelerator, or even the elevator in my dad's office building, made a mistake.

Incidentally, my uncle was the one who got me interested in science, and that trip to the hospital got me using computers for something other than games. Fast forward 24 years and...well...part of what I do is work on provably correct systems.