If that were true we'd have no cybersecurity professionals left.

In my experience, the work is focused on weakening vulnerable areas, auditing, incident response, and similar activities. Good cybersecurity professionals even get to know the business and tailor security to fit. The "one mistake and you're fired" mentality encourages hiding mistakes and suggests poor company culture.

"One mistake can cause a breach" and "we should fire people who make the one mistake" are very different claims. The latter claim was not made.

As with plane crashes and surgical complications, we should take an approach of learning from the mistake, and putting things in place to prevent/mitigate it in the future.