In Argentina, a well known case (well known within the industry) of fatal radioactive poisoning from an experimental nuclear reactor happened because an extremely experienced and well regarded operator was used to disabling safety measures of the reactor to speed things up. After all, he understood it perfectly and knew what was and wasn't actually safe to do.

Until he made a mistake, got a dose of radiation (he may have splashed himself with water, actually), and he instantly knew he was dead. And he was, within days, if my memory serves.

Experts make the dumbest mistakes because they are sure safety doesn't apply to them, because they know better.