An earthquake that was one of the largest ever recorded and resulting in one of the largest tsunamis ever as well. So you know, pretty common circumstances.
That the '1000 year tsunami' happened 40 years after commissioning is more suggestive of engineering incompetence than bad luck. And unlike bad luck, incompetence is a lot more prevalent.
You just defined bad luck. They did plan for better than a 100 year earthquake. They met those standards. Problem is sometimes you flip 10 heads in a row (equivalent to 1000 year event), when they could only handle 7.
