Nature bursts its bounds. People seethe and erupt.

Japan is among the safest countries in the world, but its headlines are terrifying. Can we send our children to school? Ride a train to work? Socialize on the Net? Set up house near a river, a mountain, a nuclear power plant?

Yes, of course. Normality overcomes tragedy, except when — very occasionally, statistically speaking — tragedy overwhelms normality.

Nature cannot be held accountable for her depredations. She answers no questions, gives no explanations. It’s different with people. They are called to account, and do explain, sometimes, though inadequately:

“I was frustrated.”

“I was angry because I could not die.”

“I was going to kill myself after killing some people.”

Those statements were reportedly made to police by young men accused, respectively, of: killing one passenger and injuring two in an unprovoked knife attack on a shinkansen in June; stabbing a stranger to death in a Nagoya manga cafe in May; and stabbing two men, one fatally, on a Hiroshima street in January.

Other crimes still fresh in the collective memory make the same point — a point known to everyone and yet perpetually shocking: that life, seemingly ours for life, so to speak, is fearfully precarious. In May, a 7-year-old girl in Niigata was murdered on her way home from school. In June of last year, a 9-year-old Vietnamese girl living in Chiba was murdered on her way to school. The suspect in the former case is a young man who had been living quietly in the girl’s neighborhood. Convicted earlier this month in connection with the latter is a one-time head of the victim’s school’s parent association, the father of a classmate, who had in the past volunteered as a crossing guard near the school. He maintains his innocence and has appealed the conviction.

Nature’s convulsions are, as it were, natural. Our vulnerability to them is ancient and must — and for that reason to some extent can — be lived with. Not so our vulnerability to the nodding acquaintance living quietly down the street, or the perfect stranger sitting across from us in a train, or sharing some other public space with us, someone who very possibly never committed a violent act before and has no reason in the world to dislike us, let alone seek to kill us, still less our children. This is something new.

And though the statistical odds are reassuringly high that, however eventful your day, you will get home tonight alive and unscathed to find your loved ones similarly unharmed, the feeling is growing that you can’t be too careful. Witness, says Spa! magazine, the recent surge in sales of such defensive implements as pepper sprays, truncheons and stun guns.

Armed or not, we must be prepared, say both Spa! and the weekly Shukan Post. Prepared how, for what? With vigilance, for anything. Anything can happen, anywhere. What would you do if? Think the unthinkable and consider it possible.

Imagine, says Shukan Post, a movie theater, pitch black; suddenly the drama is not onscreen; the man shouting and waving a crowbar is no actor, he means business. What business? He’s “frustrated,’ perhaps, thwarted, wants to die but not alone.

Who knows what business? A psychiatrist, maybe. Spa! speaks to one — Dr. Yoshiyuki Kogo — asking, “What’s the difference between a depressive whose thoughts tend toward quiet suicide and one bent on violence?”

“Revenge,” says Kogo. The latter wants revenge; the former can live, and die, without it.

It sounds plausible. Some people blame themselves for their failures, others blame society. Be suspicious, Kogo says, of people who avoid eye contact. “Without eye contact, a person is not a person but a thing — a thing on which you can project images of everyone you hate.”

Thoughts immediately fly back 10 years to the Akihabara massacre, in which 25-year-old Tomohiro Kato drove a truck through a crowd of shoppers and then flailed about with a knife, killing seven and injuring 10. He was very “frustrated” indeed — an impoverished, indebted, friendless low-pay temp worker who had just been given notice; a self-declared mobile phone addict who had posted online, “Anybody with hope can’t possibly understand how I feel.”

A person in such straits might well crave revenge — against you, if you’re in the wrong place at the wrong time. The wrong place can be anywhere. Cinemas have been attacked in the U.S. — not, so far, in Japan. Is that a reason to go to a movie with an easy mind? An easy mind can get you killed. Be alert wherever you are, urge both magazines. Before you settle down to whatever you’re doing, survey the room, or train, or bus, or plane. Know where the exits are. Seat yourself, if possible, near one.

Do you see anyone around who looks weird? What does “weird” mean? Kogo mentions averted eyes. Shukan Post instances “glaring, mumbling to oneself.” It may be harmless; it may be your imagination. Assume it is not, Shukan Post advises, and get out or edge away — knowing that in doing so you set back the long struggle for diversity, the right to be different, to seem weird, even to be weird.

It’s up to you. Do your principles outweigh your fears, or vice versa?

Male passengers in the shinkansen car that was attacked in June as it left Tokyo for Osaka came in for much tweeted abuse. They should have stormed the attacker, tweeted the armchair critics — overwhelmed him, overpowered him. Nonsense, snaps self-defense expert Hiro Kuroki, speaking to Spa!. In a situation like that, “Your mind goes blank, your body goes rigid.”

One man in fact did attempt to stymie the alleged attacker, and paid with his life. He was the bigger man, and presumably stronger, but all he had were his bare hands against a knife.

Kuroki stresses defense. Use a briefcase as a shield, an umbrella as a sword, a fire extinguisher, a seat cushion — anything — but focus on escaping, he says, not on being a hero.

“I had a teacher,” says Kogo, the psychiatrist, “who used to say, ‘There’s a Hitler in all of us.'” Or a Tomohiro Kato. Hidden in most. Surfacing in a few. Keep your eyes open, your briefcases handy. When dining out, says Shukan Post, plates make good defensive weapons. Learning to think of them as such is half the battle.

Michael Hoffman is the author of “In the Land of the Kami: A Journey into the Hearts of Japan” and “Other Worlds.”

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