I was walking home Sunday night when I happened upon the skeletal remains of Arts Fest, the erstwhile gates of which had been converted into a police barricade.

Apparently, a suspicious package had caught the eye of one of the Arts Festival’s security personnel, and shortly thereafter, the police had cordoned off much of downtown Iowa City. Then the Johnson County Metro Bomb Squad arrived in a sleek black truck and unloaded a robot that looked — if you’ll pardon a reference that was dated before I was even born — a lot like No. 5 from Short Circuit.

By the time I arrived on the scene, a conspicuously large, conspicuously gleeful crowd of onlookers had gathered at the intersection of Iowa Avenue and Dubuque Street to cheer on No. 5 as he clanked toward the offending parcel.

As a red-blooded American, robots naturally intrigue me, but I was leery about stopping to watch the bomb squad at work.

On the street, I did a little morbid number crunching. See, I typically like to keep my chance of blowing up as close to zero as possible. In this case, a number of highly trained bomb experts had determined that a suspicious package had a possibility of blowing up that was at least greater than zero.

Given that I had never before been near another object that drew the attention of a bomb squad, I reasonably concluded that I had never been more likely to blow up than I was at that moment.

But even as I nestled in the loving arms of my couch, people were still gathering around the maybe-bomb, gawking and snapping pictures. Hadn’t they done the same math I had? Didn’t the non-zero risk of exploding bother them?

Their behavior was a little reckless but certainly not without parallel. A good analogue to bomb-gawking is hunkering down before a big storm. When a major weather event — a hurricane, a tornado, a flood — threatens, evacuation orders are often ordered. Most people follow those orders and get out of the way.

But some people stay put.

When you think about it, the risk profile for a bomb-squad call and a major storm evacuation is pretty similar. The likelihood of taking personal damage in either scenario is higher than usual, but it’s still very low in real terms. Some people are willing to take their chances and absorb the risk of disaster.

To me, the behavior of the bomb-watchers and the storm-waiter-outers is explained by a simple rounding error. When people assess risk and determine that a strange package is almost certainly not a bomb, they convert their probabilistic conclusion into an absolute certainty.

Sprinkle in a little magical “not me, not here” thinking, and you’ve got a group of people who are much too comfortable pulling up a front-row seat to watch a bomb defusing robot bebop down Dubuque Street.

“It couldn’t be a bomb; this is Iowa City.”

It’s an understandable thought. We have the pleasure of living in a place where things almost never explode, but that pleasure has clearly dulled our instincts for self-preservation.

I’m not saying you should live in constant fear of crime or terrorism — that would be extremely unhealthy. I’m not saying you should stay inside and hide from the horrors that might lurk outside your windows. I’m just saying that when the bomb squad rolls up, you should hit the bricks.