I will not pretend that I know how we should have left Afghanistan. But neither do a lot of people dominating the airwaves right now. And the confident pronouncements to the contrary over the past two weeks leave me worried that America has learned little. We are still holding not just to the illusion of our control, but to the illusion of our knowledge.

This is an illusion that, for me, shattered long ago. I was a college freshman when America invaded Iraq. And, to my enduring shame, I supported it. My reasoning was straightforward: If George W. Bush and Bill Clinton and Tony Blair and Hillary Clinton and Colin Powell and, yes, Joe Biden all thought there was some profound and present danger posed by Saddam Hussein, they must have known something I didn’t.

There’s an old line: “It ain’t what you don’t know that gets you into trouble. It’s what you know for sure that just ain’t so.” And so it was with the Iraq War. Bush and Clinton and Powell and Blair knew quite a bit that wasn’t true. As Robert Draper shows in his book, “To Start A War: How The Bush Administration Took America Into Iraq,” they were certain Hussein had weapons of mass destruction. Only he didn’t. They were also certain, based on decades of testimony from Iraqi expats, that Americans would be welcomed as liberators.

There were many lessons to be learned from the Iraq war, but this, for me, was the most central: We don’t know what we don’t know, and, even worse, we don’t always know what we think we know. Policymakers are easily fooled by people with seemingly relevant experience or credentials who will tell them what they want to hear or what they already believe. The flow of money, interests, enmity and faction are opaque to outsiders, and even to insiders. We do not understand other countries well enough to remake them according to our ideals. We don’t even understand our own country well enough to achieve our ideals.

“Look at the countries in which the war on terror has been waged,” Ben Rhodes, who served as a top foreign policy adviser to President Barack Obama, told me. “Afghanistan. Iraq. Yemen. Somalia. Libya. Every one of those countries is worse off today in some fashion. The evidentiary basis for the idea that American military intervention leads inexorably to improved material circumstances is simply not there.”

I wrote a book on political polarization, so I often get asked to do interviews where the point is to lament how awful polarization is. But the continuing power of the war on terror framework reflects the problems that come from too much bipartisanship. Too much agreement can be as toxic to a political system as too much disagreement. The alternative to polarization is often the suppression of dissenting viewpoints. If the parties agree with each other, then they have incentive to marginalize those who disagree with both of them.

At least for my adult life, on foreign policy, our political problem has been that the parties have agreed on too much, and dissenting voices have been shut out. That has allowed too much to go unquestioned, and too many failures to go uncorrected. It is telling that it is Biden who is taking the blame for America’s defeat in Afghanistan. The consequences come for those who admit America’s foreign policy failures and try to change course, not for those who instigate or perpetuate them.