Well aren't you lucky! And in my experience with this question, there's a big difference between "felt fireable" and "is fireable", which also gives insight.

I have my own go-to example that I'll use if they give back your type of answer (which has happened). I messed up packaging a demo version of our software that almost sank a 300k sale (~5% of revenue on the P&L for that year).

Was I going to get fired? no Did 23 year old me think I might get fired? yes

Essentially it boils down to what's a large mistake you've made while employed (or otherwise) and how did you resolve it.

Can just rephrase the question: "tell me about you've made in your career and how you dealt with it"

(Irrelevant question) Does Octal has a url scheme to open a HN from from Safari to Octal?