Training/test divergence in chess leads to "blunder of the century"

In class, I noted that catastrophic things can happen when the training data do not sufficiently represent situations that can occur in real life -- this is often referred to as the divergence between training data and test data. An interesting instance of this happening in the real world: a high stakes human-vs-machine chess match where the position on the board was simply outside the "repertoire" of the human grandmaster.

It turns out that this has been referred to as "the blunder of the century". In blog comments immediately afterwards, one person wrote, in all seriousness:

I have a bad feeling. No, I can't believe that Kramnik really just overlooked a mate in one. It is almost a must: he may have come down with some health problem, what was able to "disconnect" his thinking (like a mini-stroke or temporary cerebral ischemia or something along that line). At this point I am concerned about his health.I wouldn't be surprised if the next news would be that he is in a hospital.

Chess enthusiasts may be interested in this detailed analysis of what happened, including, as a mentioned, analysis looking at the grandmaster's visual attention as an indicator of what he was thinking at the time.