Normal Accident
Etymology
Coined by sociologist Charles Perrow in his 1984 book after studying the Three Mile Island meltdown. The jarring pairing of "normal" with "accident" is the point: in tightly coupled, interactively complex systems, disaster is an expected feature, not an anomaly. The concept reshaped how engineers think about risk.
noun phrase · /NOR-mul AK-sih-dunt/
A catastrophic failure that is essentially inevitable in systems that are both highly complex and tightly coupled, no matter how careful the operators.
What it names
A handle for accidents that aren’t freak flukes or simple negligence but a built-in property of the system’s design — where so many parts interact so tightly that some unforeseeable combination is bound to fail.
Example
Blaming one technician missed the bigger truth — the reactor was a normal accident waiting to happen, given how tightly its systems were coupled.
Related idea
Powered by cascade dynamics and second-order effects: what makes an accident "normal" is that a small fault propagates through tight couplings faster than anyone can trace or contain it.