You’ve probably heard this one: “Guns don’t kill people, people kill people.”

For the moment, let’s assume that that’s a good faith argument and not a slogan designed to end a conversation about gun control.

OK, people kill people. But why?

A Harvard psychiatrist who spent his career working with the most violent offenders in the Massachusetts prison system thinks he figured it out: It’s shame.

Over decades of work, James Gilligan found that the men he interviewed were not motivated by rage, revenge or money when they acted violently. They knew what they were doing – they didn’t “black out” or “snap.”

But again and again the men he worked with told him that just before they acted out violently they had felt humiliated and wanted respect.

Gilligan wrote in his 2001 book “Preventing Violence,” that a feeling of shame, “is the pathogen that causes violence just as specifically as the tubercule bacillus causes tuberculosis.”

This is should be a key insight as we look at the policy response to rising violence, highlighted by repeated mass murders, including two in the last month: the racist killing of 10 African American shoppers in a Buffalo, New York supermarket, and the massacre of 19 fourth-graders and two teachers in Uvalde, Texas.

These acts of terror dominate the news, but they make up a tiny fraction of the gun violence in America. As a country, we have by far the highest rates of gun deaths in the developed world, but the violence takes many forms and is not evenly distributed geographically, so it’s hard to see a single cause.

Roughly 40,000 people die in America from gun shot every year, about half coming by suicide, with older, white men, often in rural areas, making up the majority. Gun homicides are the leading cause of death for American children and teens. About half of these killings are concentrated in about 100 cities that are home to about one-quarter of the country’s population.

What beside easy access to guns ties these acts of violence together?

Mental illness is the most commonly cited cause for gun violence (after guns), and it’s true that mental health services are expensive and hard to find in this country, especially in rural areas. There is stigma about mental illness that keeps people from getting care. In some fields, just talking to a therapist could be a career-ender.

But it’s not a satisfying explanation for what is happening.

People with mental illness are much more likely to be the victims of violent crime than perpetrators. And most violent crimes, even random mass murders, are committed by people who are considered mentally competent in court.

Gilligan’s observation about shame can both offer an explanation for many different kinds of acts and suggest a path forward. We should be able to talk about what a world with less humiliation would look like.

Everyone has been shamed at some point in their lives, but most of us never do anything violent. On its own, shame is not enough to trigger violence, Gilligan writes, just as the turbucule bacillus doesn’t cause tuberculosis in everyone who is exposed. The presence of other social and economic factors make people more vulnerable to acting violently, and there is no single lever to pull that would solve the problem.

Most violent acts are committed by young men, who also have low status in our society. They compete for the lowest-wage jobs in our economy, and have the highest unemployment rates of any age group. Our social programs disproportionally spend to help older people. In a culture that celebrates wealth, children and teens are the most likely Americans to live in poverty. This situation is even worse for Black and brown men, who also face racial discrimination on top of age-based economic disadvantage.

Everyone needs to feel productive. A society that can find a place for young people who are no longer in school is bound to be a less violent society.

Gilligan also writes that notions of masculinity and homophobia become weapons used to demean and humiliate. Gay and transgender teens have high rates of suicide. Others feel they have to use violence to prove their status as men. The evidence is mounting that the culture is not doing a good job teaching children that they do not have to meet some unattainable standard to be worthwhile.

Guns don’t cause violence, but they raise the stakes. The presence of a gun can turn a moment of despair into a suicide or an argument into a murder.

It stands to reason that reducing access to firearms would reduce gun violence, but it’s not the only thing that would make a difference.

Before the horror of this moment passes, we need to ask what else can we do about shame.