A team manager once called and asked me if anything changed in the hypervisor (I used to support and make local modifications to some virtualization software) because her team's daily data processing job failed, which previously had run with no issues and nothing changed at their end.

I commented back, maybe with a little too much confidence, that if their input file changes daily, then their program changes daily. That is, from one day to the next, it may take different paths (or a different combination of paths) through the code's logic. In that way, I claimed, her program was like a language interpreter, and her input files were like programs.

She didn't seem completely convinced, but apparently they got the job running again because there was no follow up on that particular issue.