I think it can be hard for anyone who hasn't done safety-critical software before to understand just how much testing goes into it. Even for non-human spaceflight, the stakes are so high, we have all of the testing you would expect as far as unit tests, system integration tests, end to end testing, but then we also have full human in the loop software sims, full hardware in the loop sims both at multiple levels of integration, and on and on. For every line of code I've written for a spacecraft, I'm 100% confident that if that line is responsible for a bug in flight, there are at least 10 other people who would share the blame with me.