So which one will it be?

On a more serious note: this really depends on the person in question. Not everyone has that state of mind it takes to be extra wary when you find yourself in a similar situation where it went worng before. I've worked with people who made pretty severe mistakes, were pointed out, nodded 'yes', only to just make the exact same programming mistake a few months later. And again, and again.

We all like the story of "just spent a million dollars training you", but experience tells me that there is absolutely no assurance whatsoever that any random person won't be repeating that mistake in the future.

EDIT: and to be clear, of what tiny bit I know, I blame test more than dev. From the dev side I can see someone making a stupid mistake (that for the record I could just as easily make) swapping the foo with the bar, or some mis-click in IB. But I'm still astounded that this made it out of test without getting caught.