By now, the story of Tamerlan and Dzhokhar Tsarnaev is as familiar as it is curious. Here we are, once again, trying to determine how reportedly low-key, fun-loving people from abroad became terrorists, unleashing death and suffering on innocents.
We're left wondering how these brothers moved from apparently exhibiting the flexibility that living in a diverse culture requires to engaging in such inflexible thinking that they planted bombs along a marathon route. We're left wondering how the supposedly friendly Dzhokhar, whose pals kept saying he wouldn't get involved in a plot like this, turned so abruptly that he ended up hiding in a boat with the whole world bearing down on him.
Curious, indeed. But finding answers these questions is the key to greater personal security for Americans and more geopolitical stability. Nailing down this part of the battle against terrorism is as important as all the security apparatus.
Jonathan Haidt's book, "The Righteous Mind: Why Good People are Divided by Politics and Religion," is a good place to start exploring how people's thinking can grow so rigid that they turn to killing and maiming people.
For one thing, he writes, larger groups can contribute to such rigidity. In the case of the Tsarnaev brothers, Chechen terror groups may have played a role in their entering a mental lockdown.
Rigidity also can fester when we disengage from the hard work of persuading another to our point of view. Persuasion is hard because it is risky.
Haidt explains that persuasion requires understanding the other person's moral intuitions. And that's scary because it could change our own beliefs. Writes Haidt, a professor of ethical leadership at New York University's business school:
"If you really want to change someone's mind on a moral or political matter, you'll need to see things from that person's angle as well as your own. And if you truly do see it the other person's way - deeply and intuitively - you might even find your own mind opening in response."
Such thinking is the opposite of the righteous mind, which, in political and moral arguments, Haidt writes, prefers going into "combat mode." He concludes that "empathy is an antidote to righteousness."
Haidt's conclusion resonated as I read what the older Tsarnaev once told an interviewer: "I don't have a single American friend. I don't understand them."
What a revealing statement. I don't understand them. Talk about lacking the capacity for empathy. His mind had hardened to where it, literally, went into combat mode.
The Tsarnaevs' story is distressing, but let's not despair. Examples abound of people who have moved from the hardened thinking of their group, either politically or religiously.
Look at the Arab Spring, which was largely a response to oppressive governments by dissidents thirsting for freedom. A good example of the latter is Abdel Basset Ben Hassen, whose work is profiled through the George W. Bush Institute's Human Freedom Project.
The Tunisian has spent his adult life promoting human rights in the Arab world. He's trained activists in ways to promote freedom and he has resisted authoritarian governments in Africa and the Mideast.
Also reassuring is that many formal and informal interfaith groups have formed since 9/11. The participants gather to better understand why others believe the way they do.
These discussions happen at the clergy level, among rank-and-file believers and through the linked-in nature of the Internet.
Still, the rigidity that came over the Tsarnaev brothers remains a troubling reality. It led them to decide that murdering and maiming was better than persuading.
There really is no easy way to curb that toxic combination. It is a fact of life in a world where the righteous mind can build his own arsenal.
But we must keep naming the demon so we understand it better. And we need to keep working on expanding networks to bring in those we don't understand and who don't understand us. This is part of the moral capital that Haidt says communities need to make cooperation possible.
The bombing in Boston revealed that this part of the fight against terrorism is hard to perfect. But we must keep dealing with it to keep the combat mode of the righteous mind from kicking into action again.
William McKenzie is an editorial columnist for The Dallas Morning News. Readers can email him at firstname.lastname@example.org