When Americans hear what might be gunshots, we run. Of course we do.

“Shooter! Shooter!”

Police shut down Los Angeles International Airport’s central terminal on Sunday, after a loud noise prompted panicked passengers to self-evacuate. People scattered, dove under seats, and ran—they thought—for their lives.

We are all primed to run.

Over the past few weeks, crowds fled loud noises perceived as gunshots in malls in Florida, North Carolina, and Michigan. Frightened faces in videos and photos posted online gave an air of substance to unsubstantiated rumors. We’ve been conditioned by enough images of crowds fleeing actual guns that it’s almost sensible to assume a cascade of terrified people running in one direction means there’s a madman with a gun behind them.

I know I would run.

There was a time when I would’ve assumed a loud bang in public was a balloon popping or car backfiring—before the assumption of mass shootings was reasonable. The Columbine massacre happened one year after I graduated from high school, so I was spared the first clouds of fear that spread in waves over our nation’s schools. And I was long out of college by the time 32 people died in the shooting at Virginia Tech.

Fear of random death first gripped me when I lived in D.C.’s suburbs. It was 2002 and John Allen Muhammad and Lee Boyd Malvo had started picking off their victims: people running mundane errands like pumping gas, walking across parking lots, mowing the lawn. Soon, I developed a mental checklist of public places to avoid.

One witness thought shots came from a white box truck. You don’t realize how many white trucks are on the road until you start to suspect that every one of them is loaded with a monster packing assault rifles.

After driving my tank down to empty one day, I forced myself to stop for gas. I quickly shoved the nozzle, trembling in hand, into my tank, and jumped back into the driver’s seat to wait. With every white vehicle I saw driving past—box truck, pickup, car—my breath caught in my throat.

Then I heard a pop.

Heart pounding, I ducked until in the eerie quiet I realized I had just heard the pump’s automatic shut-off feature.

The Beltway snipers were active for mere weeks in October 2002, and after police arrested Malvo and Muhammad, I tried to unlearn my fear. People started letting their kids plays outdoors again, shopping as normal, pumping gas. The shooters had actually been driving a blue Chevy Caprice. Our collective fears of white box trucks were unfounded, a misperception-turned-sign of impending doom.

But I still understand this visceral impulse to scream and run (and ask questions later) that so many people across America have today. When those of us living around D.C. were terrorized by random shootings, there was a sense that you could stay safe by avoiding places the gunmen had struck before. I know many people who’ve applied this logic to other public spaces after the multitude of mass shootings in recent years: No more watching movies in theaters, no more dancing in night clubs.

We exist in a realm of shadows. We are a nation terrorized.

“We exist in a realm of shadows. We are a nation terrorized.”

Shortly after 9/11, there was a time when public sentiment encouraged a sort of audacious boldness and popularized a refusal to fear. We would rebuild bigger, better, stronger because our enemies could not stifle the courage of the American people. Perhaps it was easier to lean together when we assumed our enemies were outsiders.

But since then, we’ve experienced other forms of terror. There have been near constant reminders that mass shootings can happen anywhere, readily and easily, with weapons in the hands of colleagues and neighbors. No matter where a shooting happened yesterday, another could happen where we are today.

As journalist C.J. Chivers wrote in his history of the tools of modern terror, “Acts of crime, terror, and oppression with Kalashnikovs and AR-15 descendants, endured by civilians under withering fire, have been hard-wired into our times. There is no end in sight.”

We have learned, thanks to the immediacy of violent images on social media and the constant, impending horror of wondering where will be next, that I could be next.

And so, if we can, we run.

Sarah Stankorb’s articles and essays have appeared in The New York Times, The Washington Post, Slate, The Atlantic, and Salon. She also regularly contributes to CNNMoney and GOOD Magazine. Sarah’s beat spans social enterprise, women’s rights, the environment, health, motherhood, religion, and cultural commentary.