A bad event occurs. There are usually multiple checks and balances, controls and personal responsibilities, which fail for the event to happen. That's why the event doesn't happen all the time. It might not happen for 10 years, or 20 years. Maybe one or two of the controls would fail, but the other controls would prevent the event from occurring. But, the event probably will happen at some point, and then everyone seeks a single point cause, maybe a single person to blame, when really, it is multiple causes, or multiple controls which all just happened to fail at the same time.
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