At my first development job (paid internship at a moderately-sized, though fast-growing business - maybe 300 people at the time?) I introduced a bug that didn't appear until a certain microservice stopped working (my code defaulted in the wrong direction when the ms failed) and as far as I can tell they may have lost or almost lost a pretty big account from it. In an after-hours meeting regarding the issue, one of the higher ups ended up storming out and never showing up again.

In my defence, we had to get 2 PR approvals before anything was merged! But I definitely learned a thing or two from that experience