In the movie "The Fog of War," Robert McNamara, U.S. Secretary of Defense  during the Vietnam War (’60-’67) takes stock.

At my age, 85, I’m at age where I can look back and derive some conclusions about my actions. My rule has been try to learn, try to understand what happened. Develop the lessons and pass them on.

One key lesson is the centrality of disagreement, even with similar information and mutual respect:

The other photograph, you can just see me saying: "Jesus Christ, I love this man, I respect him, but he’s totally wrong. What am I gonna do?"  Johnson couldn’t persuade me, and I couldn’t persuade him. I had this enormous respect and affection, loyalty, to both Kennedy and Johnson. But at the end, Johnson and I found ourselves poles apart.

McNamara concludes it is irrational to disagree with similarly qualified majorities:

What makes us omniscient? Have we a record of omniscience?  We are the strongest nation in the world today. I do not believe that we should ever apply that economic, political, and military power unilaterally. If we had followed that rule in Vietnam, we wouldn’t have been there. None of our allies supported us. Not Japan, not Germany, not Britain or France. If we can’t persuade nations with comparable values of the merit of our cause, we’d better reexamine our reasoning.

On some subjects he choose silence, which many will take to be a bad sign:

Errol Morris: After you left the Johnson administration, why didn’t you speak out against the Vietnam War?

McNamara: I’m not going to say any more than I have. These are the kinds of questions that get me in trouble. You don’t know what I know about how inflammatory my words can appear. A lot of people misunderstand the war, misunderstand me.

I’d like to see a sequel, "The Fog of Bank," about his thirteen years as President of The World Bank.