I’ve heard the word “stereotype” all of my life, but I only recently learned where it came from.

It’s a term from the printing trade. A stereotype is a papier mache impression of a block of type used to cast hot metal into plates for a printing press.

It was the technology that enabled low-cost mass production of books, magazines and newspapers in the early 20th century, giving people all over the world the ability to read the same thing at almost the same time. (It was sometimes known as a “cliche,” another word that’s come to mean something else.) The word was first used in the way most of us know it – a rough summary of characteristics of a stranger or a group of people – by the newspaperman Walter Lippmann, who described psychological stereotypes in his 1920 book “Public Opinion.”

“For the most part, we don’t first see and then define, we define first and then we see,” he wrote. “In the great blooming buzzing confusion of the outer world we pick out what our culture has already defined for us, and we tend to perceive that which we have picked out in the form stereotyped for us by our culture.”

We don’t have much choice, Lippmann says. It’s hard enough to really get to know yourself or the people you love; you couldn’t know the full truth in all of its complexity about millions of strangers, too. I need generalities to rough sort the mountain of information I contend with, and I accept that people may need to make generalities about me, or “people like” me, at times as they make their way in the world.

I felt myself reaching for a stereotype Monday morning, when I heard that there was a mass shooting in Las Vegas. My first thought was, “Please, don’t let it be a Muslim.”

Why? Easy. I was afraid that if the shooter had been a Muslim, innocent Muslims in my community would be bullied in school or hassled on the street more often than they are already. Maybe a lot more.

If the shooter had been a Muslim, the same people who are saying today that it’s too soon to politicize this violence, from President Trump on down, would be demanding deportations and immigration bans.

I was afraid that innocent Muslims would be stereotyped. I doubt that I was the only one who felt that way.

But it looks like the shooter wasn’t a Muslim (despite a piece of fake news expertly pushed by ISIS). It looks like he was a white guy with no religious or political agenda, who’d quietly stocked up enough guns and ammunition to shoot more 500 people in a matter of minutes.

There have been a whole run of stories that probe into why he would commit such a horrible crime. That probably would not have been necessary had he been Muslim. Then his motive would not have been considered such a mystery because a stereotype would have provided the answer.

So, I admit it. I was relieved for a second when I heard the identity of the killer in Las Vegas. I knew that this meant that people were going to view this event through a frame that would make me more comfortable.

We would probably end up talking about gun control and mental health services instead of Immigration and Customs Enforcement crackdowns and hate crimes. White kids were not going to get hassled at school. White ministers were not going to be bullied into renouncing violence.

But the relief hasn’t lasted long.

Stereotypes might help you process information quickly, but they can also make you blind to the thing that’s right in front of your face. In this case, that thing is really ugly.

Race, religion and identity dictate what we see and how we see it. There are different sets of consequences for different people.

Even mass murder can be more or less troubling depending on who the mass murderer is.

It’s easy for me to see it when other people do it, but not so easy to see when I do it myself.

“For the most part, we don’t first see and then define, we define first and then we see,” Lippmann wrote in 1920.

After what was supposed to be a century of progress, it’s unfortunately still true.

Greg Kesich is the editorial page editor. He can be contacted at:

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Twitter: gregkesich