You're right (and I think commenters saying that parent was talking about halting problem are wrong - it was clearly about chaotic systems, which are deterministic). And yet, this doesn't make the original statement - "we have no idea what happens in our own code" - any less true. Without even touching the halting problem, all code we write quickly explodes in complexity beyond our ability to mentally simulate it, and those of us who don't work on life critical systems are not paid for anything more than some unit tests and a cursory "uh, it looks ok to me" assessment.