There is a moment, a mere moment, when Donald Rumsfeld’s eyes well up and he chokes a bit. This comes in Errol Morris’ documentary “The Unknown Known,” in which Rumsfeld mentions visiting the wounded of the Iraq War. It is then that we get a glance at the man behind the word-playing frat boy who should not be able to sleep at night but from all the evidence does -- soundly. Socrates said the unexamined life is not worth living. Maybe. But in Rumsfeld’s case, it is certainly worth watching.

Morris takes his title from a famous bit of Rumsfeldian repartee with the media. In February 2002, he was asked by NBC’s Jim Miklaszewski if there was “any evidence” linking Saddam Hussein’s regime in Iraq with “terrorist organizations.” Rumsfeld replied, “As we know, there are known knowns; there are things we know we know. We also know there are known unknowns; that is to say we know there are some things we do not know. But there are also unknown unknowns -- the ones we don’t know we don’t know.” This was very cute, but hardly a reason to go to war.

Morris had earlier done a documentary on Robert S. McNamara, the Vietnam-era defense secretary. “The Fog of War” was a much more satisfying film because McNamara opened an intellectual vein and bled second thoughts, regrets and insights in frame after frame. It was elucidating and moving.

Rumsfeld, in contrast, has virtually nothing to say. His entire approach has changed little from when he was asked in 2003 about widespread looting in Baghdad: “Stuff happens.”

It is this quote, much more than the whimsical one about knowns and unknowns, that comprises the guts of the indictment of Rumsfeld. He was not the president and so the war was not his. But what happened after the war was supposedly over was a different matter. Rumsfeld’s Pentagon ran the place, and things just fell apart. Stuff kept happening.

I was touched by Rumsfeld’s compassion for wounded troops. But he showed no interest at all in the many Iraqis who died in internecine violence after Saddam’s statue had been toppled in Firdos Square. “Stuff” and “stuff” and more “stuff.” The Iraqi army was disbanded, and armed young men roamed the country. The secretary of defense stood back from it all like a kindergarten teacher keeping an eye on the sandbox.

More than 4,400 Americans were military casualties in Iraq. The figures for Iraqis are all over the place, but it seems at least 100,000 civilians -- but maybe many more -- perished. And of course, the killing continues. This is all largely a consequence of the war and the breathtakingly incompetent way the U.S. handled the post-”mission accomplished” period. It seems that not much attention was paid to what would happen after Saddam was ousted and his army defeated. It was as if the people of Iraq did not matter.

What followed was an incalculable disaster. The world was rid of one dictator, but that was scant consolation for the devastation of Iraq and the concomitant rise of Iran. In America, the war provided ample reason for many to embrace isolationism. The U.S. does nothing in Syria because it did the wrong thing in Iraq.

Aside from that one twitch of emotion over the wounded, Rumsfeld appears to be a man so stuck on himself and his buoyant cleverness that he cannot accept fault or even entertain the notion. He sat down with Morris for a total of 34 hours because a documentary was just another chance to preen.

The Iraq War remains a mystery: What were we thinking? Why that obsession with Saddam? Why were we suddenly so spooked about chemical weapons when they had been around since the Second Battle of Ypres in 1915? Why didn’t we factor in Shiite-Sunni enmity and what the disestablishment of the Baath Party might do?

Why? Why? Why?

Rumsfeld could have answered those questions. But he is a most incurious fellow. (He could not even supply Morris with a lesson from the Vietnam War: “Some things work out, some things don’t. That didn’t. If that’s a lesson, yes, it’s a lesson.”) He is not in denial, which is passive and defensive, but in an aggressively selfish refusal to say what he knows -- what he must know. He talks of things known and unknown and then frog-marches us into a semantic quagmire in which there is no such thing as truth. He weeps for the wounded, as well he should. They had the courage to face the enemy while he, in contrast, cannot face the truth.

Richard Cohen is a writer with the Washington Post Writers Group. He can be reached at cohenr@washpost.com.