That was the result of fautly risk assesment. If you are always cheery and endlessly optimistic, chirping birds will sing along with you as you skip down the flowery, sunlit path. You will also get lulled into making fatal errors like " That won't happen to me." or "That can't happen, here."
Yep, it's called "hubris". When we do or build things in regards to natural events, we seem to have an attitude of "What's the worst that can happen?" Well, mother nature has nasty way of demonstrating exactly the worst that can happen.
New Orleans was a prime example of that. The berms and dykes around the city were supposed to be something like 20 or 30 feet taller than they were but some bean-counter, in a bid to save money, decided to reduce the height because, "What are the chances of a CAT 5 hurricane slamming into NOLO?" Nature heard and responded, "Pretty damn high."
"To err is human", to get a second (and third) opinion or to get someone else to check the work is mandatory. Intelligent people make mistakes.
It was a male brain (belonging to a person who dropped out of school) who came up with the Theory of Relativity. Why has no female brain come up with such a thing?
"Tsunami? Hunh? How do you say that in Japanese?"
Any reactor design that requires emergency cooling water to be pumped uphill during a crisis by electric motors is inherently dodgy and shouldn't have made it on the first design draft.
Blame those cheap, generic G.E. reactors that the Yanks sold-door-to-door, back then.
Um, the facility is right on the coast at shore level. Why would they need to pump cooling water uphill?