Despite its well-known penchant for preparedness, Japan proved surprisingly vulnerable to a spate of disasters following a 9.0 magnitude earthquake on March 11. Nearly 15,000 people died, thousands of buildings were damaged or destroyed, and officials are only now getting a handle on the shattered nuclear plant at Fukushima. Millions have been left without electricity and water.

Perhaps more frightening than the toll extracted by the mammoth earthquake and tsunami is that the price was paid by what’s considered one of the most disaster aware nations in the world. When strict building codes, early warning systems, and a well-informed, compliant public don’t ensure disaster safety, what’s gone wrong?

The answer, on one hand, is nothing. The Japanese disasters were immense, and had they happened elsewhere, experts say damage and loss of life would have been much greater. But it’s also a mistake to think that all the losses were inevitable.

“Some brief arguments regarding the relative success of Japanese disaster preparedness can still be mentioned,” writes Harvard postdoctoral researcher Jonatan Lassa in the Jakarta Post. “First, its coastal towns and cities are often densely populated, which … means there is a higher level of exposure to disaster risks. Second, the recent Japanese disasters were not simply a problem because the disaster prevention/mitigation failed, but because there are limits to prevention and mitigation—especially when the exposure to risk is neither reduced nor considered.”

Put more directly, people often live where they shouldn’t, and that happens for a variety of reasons. Perhaps the most under-examined is the loss of “disaster memory,” as New York Times environmental writer Andrew Revkin terms it.

“It seems that just about everyone immersed in disaster preparedness and risk mitigation has an example of communities quickly forgetting wrenching lessons from past disasters,” he wrote in a 2008 article on the concept.

This was certainly true along the Japanese coastline, which is strewn with ancient markers that have warned generations of people of tsunami danger.

“High dwellings are the peace and harmony of our descendants,” a stone marker near Aneyoshi reads according to the Associated Press. “Remember the calamity of the great tsunamis. Do not build any homes below this point.”

The small village paid attention and survived the most recent tsunami, but many more don’t. Nor do they have the collective memory needed to give them a strong sense of the danger.

“It takes about three generations for people to forget,” Tohoku University Disaster Planning Professor Fumihiko Imamura told the AP. “Those that experience the disaster themselves pass it to their children and their grandchildren, but then the memory fades."

That’s unfortunate, because there are indications that warnings transmitted person-to-person go much further than all the safety drills and public service messages combined. A “megastudy” examining human behavior related to risk determined that people are more likely to engage in risk avoiding behaviors if they see others they know do it, said former Natural Hazards Center Director Dennis Mileti, who worked on the study.

“It’s cues; seeing other people take action,” he said in a recent presentation of the results. “A brilliant social psychologist a hundred years ago described this basic scientific tenet as ‘monkey see, monkey do.’”

Without that relevancy, warnings can easily fade into the daily information barrage. This is especially true after a lull in hazard events, such as the “roughly 40-year period of relative seismic calm,” that existed before this decade, Revkin points out in a recent article on Fukushima.

It’s then that people forget to assess their living conditions, communities forget and allow building in risky areas, and governments forget that one catastrophe can demolish the progress something like a nuclear power plant creates. And in culture after culture, once that forgetfulness sets in, it’s only a matter of time before the dangerous status quo returns. “I always told my parents it was dangerous here,” Hiroshi Kosai, whose parents died when the tsunami hit his home town of Natori, told the AP. “In five years, you'll see houses begin to sprout up here again.”