Unfortunately aviation safety is concerned with those 0.001% probabilities, because many of them tend to gang together and cause fatal accidents. Just like the sterile cockpit environment rule. What is the chance of some random thing being missed because the pilots were talking about an upcoming football game during landing, and moreover what is the chance of that oversight causing a real accident?

It's really, really, really small, with millions of successful flights done without problems. Yet accidents like those have happened, and have been prevented after that rule was put in place.

I was using mathematical proofs as an example of why in IT security, often times since you can't be sure, you do the proactive thing and don't run services exposed to the internet. If you have a database with credit card numbers, you don't let the DB listen for connections on a public IP, not because you think there is a security hole in the DB, but because you can't be sure there isn't.