Once again we have been reminded of the commonplace heroism that so many people hold quietly at the ready out of their compassion for others.

Two armed teenagers bent on carrying out a massacre invaded STEM School Highlands Ranch in Colorado on Tuesday.

Life-saving courage was shown by a school security guard who ran toward the sound of gunfire and apprehended one of the assailants.

At least the guard, a Marine veteran, was armed.

Teenaged students Kendrick Castillo, Brendan Bialy and Joshua Jones were not when the second thug entered their classroom. They leapt up from their desks and rushed the assailant, a classmate.

They disarmed him, beyond any doubt saving many lives.

But in the process, Jones was shot twice. Castillo was killed.

It all happened less than 10 days after another murderer engaged in a shooting spree at the University of North Carolina. There, college student Riley Howell saved lives, too.

And he, too, perished.

The loss by violence of any human being is a terrible thing. Precious lives are taken away forever.

But Bialy, the Colorado hero who escaped being shot, had an interesting, profound take on what happened. In comments to a reporter, he referred repeatedly to the attackers as cowards.

Then, he said this: “They lost. They completely and utterly lost to good people.”

In important ways, he is correct.

First, Castillo, Jones and Bialy — not the assailants — quickly became the big story of what happened at the Highlands Ranch school.

Second, they and the brave security guard prevented the attackers from carrying out the much bloodier slaughter they appear to have planned.

Third — and most important — they, Howell and other heroes of similar events remind us that while evil exists in our midst, compassion and courage are far more common.

The Colorado assailants’ names have been reported in news stories. But you will notice that in this commentary, we did not name them.

That is because who they are is entirely irrelevant.