Of the many lessons to emerge from the horrific killing of 50 Muslims as they worshipped at two mosques in Christchurch, New Zealand last Friday, the most powerful came from the nation's prime minister, Jacinda Ardern, at 38 one of the world's youngest world leaders. 

She showed her sympathy and solidarity with the shocked and grieving Muslim community by the simple acts of donning a hijab (head covering) when visiting with them and beginning her breathtaking speech to the nation's Parliament on Tuesday with the Arabic greeting "As-Salaam-Alaikum," literally "Peace be unto you." 

But then, in her speech, she did something extraordinary and rare. She deliberately did not name the 28-year-old Australian man who murdered so many of her fellow citizens and she asked everyone else not to say his name either. Here's how she put it:

"He will face the full force of the law in New Zealand. The families of the fallen will have justice. He sought many things from his act of terror, but one was notoriety. And that is why you will never hear me mention his name. He is a terrorist, he is a criminal, he is an extremist--but he will, when I speak, be nameless. And to others, I implore you, speak the names of those who were lost rather than the name of the man who took them. He may have sought notoriety, but we in New Zealand will give him nothing, not even his name." 

It's a powerful idea, and one we don't act on often enough. Just think of how many serial killers or mass murderers you can name, from the Oklahoma federal building bombers to the Boston Marathon killers to the man who opened fire on the audience at an Ariana Grande concert in Las Vegas, and so many others. Too many others.

We know all about these killers because we find them fascinating. Especially because they are so often described by the people who knew them beforehand as quiet, gentle, unassuming, good neighbors. No one could have guessed what evil lurked inside. It makes us wonder: Could one of our own neighbors commit such acts someday? Could we commit them ourselves, if something bad enough happened to us? We want to get inside the killer's head, understand the killer's viewpoint, and walk in the killer's shoes.

We're not so fascinated with the victims because we already know who they are--ordinary people just like us who happened to be in the wrong place of worship, or attend the wrong concert, or work in the wrong office. Victims of hatred and random chance who were unluckier than we are. We already know how easily we could run into the same bad luck, and how little we can do to guard against it.

But our fascination with the perpetrators of these horrible crimes makes the world a worse place than it needs to be. Ardern is right. Whoever these people are and whether they face jail, or the death penalty, or die while committing their crimes, what they want most is to be known and remembered. As if to underscore the point, the Christchurch shooter published a manifesto online and then apparently recorded his rampage with a helmet-mounted camera, live-streaming it over Facebook. (Both have now been taken down.) To refuse to say or write his name, to withdraw the attention he craves, is the only effective way to punish him.

Much more important, it may be of the few ways there is to discourage violence like this in the future. There's a reason serial killers often have copycats. The high school students who killed 13 other people and themselves in Columbine, Colorado in 1999 were apparently trying to beat the body count of the Oklahoma City bombing four years and one day earlier. Knowing their ideas wouldn't be shared and their names wouldn't be spoken or remembered could do a lot to undermine that kind of motivation.

It doesn't just apply to killers. Next time you're locked in conflict with someone--a fierce competitor, a rival for for a job you want, a difficult boss, or even a troublesome family member--think about how often you say or think that person's name. Every time you do, you make him or her bigger and yourself smaller. We know from the movie Beetlejuice, the book The Secret, and countless others, that the more you focus on something, and the more you name it, the more power it has. Refusing that attention by focusing on yourself or someone else takes that power away. It's one of the best ways there is to cut an antagonist down to size.

Our age of too much media, too much social media, too much sharing and posting and blogging and tweeting has been referred to as the attention economy. Some say human attention is today's most hard-to-obtain resource. So be careful what you do with that resource. Don't give it away to someone who doesn't deserve it.

Instead, here's a video of Christchurch high school students performing haka, a Maori ceremonial dance often associated with war, but also used to honor guests or--as here--to commemorate the dead. Some of these students' classmates were killed in Friday's shootings, and they perform the haka, in perfect sync, with precision and emotion. "Our hearts are heavy but our spirit is strong," Arden said in her speech. You can see it in every one of these faces.