If Lesson 7 shows us that is that we perceive, not see, reality, then his next lesson is how to fix that problem. We are not omniscient. We make mistakes. We can’t trust ourselves. If this is the case, then McNamara suggests we be prepared to re-examine our reasoning.

One part of re-examining our reasoning is remaining open-minded when making decisions. If we know we are not perfect, we should remain realistic about the chance of being wrong. Bring in people who disagree. Listen to them. If their questions can’t be answered, there is a good chance you are headed down a wrong path. This was certainly the case with the 2003 Invasion of Iraq when President Bush, Vice-President Cheney, Secretary of Defense Rumsfeld, and other national security advisors sidelined Colin Powell, Richard Armitage, and others in the State Department who disagreed that Saddam Hussein possessed weapons of mass destruction or links to Al-Qaeda.

Another part of this lesson is listening to our allies. McNamara’s belief is that the United States should never apply political, economic, or military power unilaterally. We should never act alone. He does not say this because he thinks defending our nation requires international deliberation or the permission of our allies. He simply believes that “if we can’t persuade nations with comparable values of the merit of our cause,” then there is a good chance we are in the wrong.

During the Vietnam War, none of our NATO allies supported us. The British refused to help. The French, who had been embarrassed by the Vietminh a decade earlier, refused to help. Japan refused help. Only Australia and a handful of smaller nations, probably with ulterior motives, sent combat troops to assist American forces in Vietnam.

In Iraq, we again brought the Australians with us. We twisted the British’s arms into helping. A handful of NATO nations joined us. No France. No Japan. No Russia or Middle Eastern nations that had supported our first foray into Iraq twelve years earlier.

This is why the United States should not intervene in the Syrian Civil War without full NATO support. This is why the United States should work through the United Nations to apply sanctions against North Korea. This is why military action should not be taken against Iran without Security Council approval. If we cannot convince anyone else that we are right, we’re probably wrong.

Find me someone who still, given what we know now, send troops to Vietnam in 1964 or Iraq in 2003 and I’ll show you a hardliner or a fool. When we ignore the overwhelming opinions of our allies, bad decisions are made and people die unnecessarily. It’s never too late to avoid a bad decision, which is why we should always remember our fallibility and remain willing to measure twice before cutting.

Jump to a lesson:
Introduction
Lesson 1: Empathize with Your Enemy
Lesson 2: Rationality Will Not Save Us
Lesson 3: There’s Something Beyond One’s Self
Lesson 4: Maximize Efficiency
Lesson 5: Proportionality Should Be a Guideline in War
Lesson 6: Get the Data
Lesson 7: Belief and Seeing Are Often Both Wrong
Lesson 8: Be Prepared to Re-examine Your Reasoning
Lesson 9: In Order To Do Good, You May Have To Engage in Evil
Lesson 10: Never Say Never
Lesson 11: You Can’t Change Human Nature
Conclusion