All it took was one careless nuclear technician to push the reactor to its limit in a poorly managed stress test to cause the explosion.

Yerrecti-bapha-whatsist-doi-hukki-whah?

No. No. No. No. No. No.

Complex systems fail in complex ways.

The people who designed the reactor did not tell the people who built the reactor about the inherent design flaws. The people who built the reactor could not tell the people who operated the reactor about the inherent design flaws AND also did not tell the people who operated the reactor about the shoddy construction. The people who operated the reactor were first, poorly trained, and second, ill-informed about both the design flaws and shoddy construction.

Those who administered the entire plant were completely in the dark about design flaw, shoddy construction and poorly trained/ill-informed operations AND under political (not technical) pressure to get the tests done.

It is not — at all — a case of ‘one careless nuclear technician.’ There is not one technician — in the entirety of all technicians who ever lived — who could be careful enough to survive that scenario. That’s why, in the series, they were very careful to state, unequivocally, that the problem would recur, unless fixed.