There could be a lot more going on than just the job. Maybe they were already burnt out from the previous job. Maybe there was serious depression or anxiety. Maybe there was a family crisis or a recent death. Maybe they'd been suicidal for months. Maybe it was all of the above. Heck, holding down a demanding job with a crappy culture when dealing with a serious mental illness is the definition of resiliency - eve if it's just for three months. 

And who says it flat out broke them? They had a really, really bad day. And survived - and got help.

What's the difference between that and getting run down and really sick for a few days?