Confirmation Bias and The Danger of Absolute Conviction

What a 1940 military blunder teaches us about confirmation bias and why intelligence acts as an amplifier, not a filter.

German armor advance in May 1940

Article Highlights

• The Historical Mirror: French military command failed in early 1940 from an unwillingness to abandon counterevidence to a long-held assumption.
• Intelligence isn't immunity: Sophisticated thinkers are often more susceptible to confirmation bias, usually constructing "better" rationalizations.
• Intellect amplifies: Without explicit checks, brainpower simply increases confidence in flawed assumptions.
• The Danger of Absolute Conviction: Unshakeable certainty is rarely proof of a sound thesis. More often, it signals that a cognitive bias has taken over.
• Seek intelligent dissent: If you can't articulate the strongest counter-argument to your position, you don't fully understand the risk.

Germany launched its western offensive on May 10, 1940. Within two days, Allied reconnaissance pilots were sending back frantic reports: thousands of German tanks, armored vehicles, and supply trucks were backed up in massive traffic jams along the narrow roads of the Ardennes forest, heading straight for the French border.

French High Command largely dismissed the reports as panicked exaggerations. Certain that the primary invasion would occur through central Belgium, senior commanders treated the Ardennes activity as a secondary effort and were slow to move reserves to meet it.¹

Decades of military doctrine had convinced high ranking officials that the Ardennes was too dense for armored forces to navigate quickly and effectively. Even if German forces attempted a crossing, their progress would be slow enough that France would have ample time to redeploy defenses. Anchoring their entire strategy to a repeat of World War I, they left the Ardennes region lightly defended.²

By May 13, German forces emerged from the Ardennes, reaching the Meuse River in just three days. At Sedan, the thinly defended French lines buckled under the assault, allowing German armor to sweep west and encircle the Allied armies to the north. Had Allied aircraft struck those jammed tank columns in the forest, or had French forces launched an immediate counterattack at Sedan on May 13–14, the trajectory of World War II may have looked entirely different.³

Reading about France’s World War II defense strategy begs the question: How could French leadership let this happen? How could they ignore direct intelligence and allow the German army to roll through the French terrain virtually unopposed?

At the root of France's swift collapse was a failure of interpretation known as confirmation bias -- the tendency to search for  and favor information that confirms prior beliefs while discarding evidence to the contrary.⁴ French war planners clung to an outdated blueprint for military strategy that they were unwilling to abandon, and it cost them everything.

The lesson extends far beyond military strategy. The beliefs we hold will inevitably be wrong at times, whether we're navigating financial markets, economic trends, or daily life. An investor convinced that tech stocks could only go up in 1999, or that the housing market was bulletproof in 2006, read counterfactual evidence the exact same way French High Command read intelligence reports: as noise to be explained away.

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How Confirmation Bias Shapes Human Belief

First, I want to talk about why confirmation bias exists: because humans love shortcuts.

As it turns out, our brains favor mental efficiency and internal consistency. Processing new information requires cognitive effort, so the brain naturally takes the path of least resistance: accepting data that fits what we already know and filtering out the rest.⁵

Because re-evaluating our core assumptions (and whether or not they are correct) is an uncomfortable practice for our minds, we routinely rely on three distinct operational filters:

• Selective Exposure (What We See): We seek out environments that reinforce our current perspectives. This manifests as tailoring media feeds, news outlets, and social circles to ensure our existing worldviews face minimal resistance (a.k.a. echo-chambers).⁶
  
  
• Selective Interpretation (How We Process): When neutral or ambiguous information enters the picture, we mold its meaning to align with our own views. For example, if someone receives a neutral email from a superior at work, it can be interpreted as praise by a confident employee or as criticism by an anxious one, depending entirely on their baseline assumption.⁷
  
  
• Selective Memory (What We Recall): Memory is reconstructive. We tend to retain information that supports our past decisions while gradually forgetting or rationalizing details that contradict them.⁸
  
  

These patterns influence how people navigate career paths, personal relationships, and everyday decision-making. Humans naturally act as narrative-builders rather than neutral observers, much like the saying: “You are the author of your own life”. 

The Financial Cost of Cognitive Filtering
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While confirmation bias occurs across all areas of life, applying this tendency to financial decisions introduces a specific risk: financial markets operate on objective data, regardless of personal expectations.

When our biases influence our money decisions, outcomes can carry significant consequences:

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Why Higher Intelligence Doesn't Protect Us

It is tempting to view confirmation bias as an issue of education or literacy, as if it only applied to casual observers. However, research consistently reveals the opposite: higher intelligence, domain expertise, and analytical ability do not protect us from confirmation bias.⁹ In fact, being more educated can often make us more susceptible to it.¹⁰

When someone intelligent forms a strong conviction, their cognitive skills don't automatically make them more objective. Instead, those skills are frequently weaponized to build a “better” defense for what they already believe.

Weaponized Logic

An individual with deep analytical capacity is usually very skilled at finding patterns, constructing arguments, and interpreting complex data. When hit with counter-evidence, a novice might simply ignore it. A highly sophisticated individual, however, has the intellectual ability to dissect that counter-evidence, identify caveats, and explain away why the data "doesn't actually apply" in this specific case.¹¹

In behavioral economics, this concept is closely tied to overconfidence (the tendency to hold an inflated view of our own judgment and abilities).¹² The smarter someone is, the more plausible, detailed, and convincing their false narrative becomes!

The High Cost of Being Wrong

For professionals, specialists, and experienced individuals (i.e. a seasoned investor or economist), confirmation bias is further amplified by ego and identity. The more time, prestige, or money an individual has poured into a public stance or a specific thesis, the higher the psychological cost of admitting an incorrect thesis.¹³

Think of it this way: intellect and experience function like an amplifier, not a filter. Without explicit systems to test our assumptions, higher intelligence simply allows us to be wrong with greater precision and higher confidence.

This is essentially why we need something equivalent to the scientific method in our everyday lives.

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How to Counter Confirmation Bias

Simply knowing that confirmation bias exists isn’t enough to rein it in.  Telling yourself to "be more objective" fails when ego (or money) is on the line.

To overcome the brain’s default programming, we need deliberate pain points that force us to examine counterevidence before making significant decisions. Here are four practical frameworks designed to stress-test your strongest beliefs and assumptions in life.

1. Run a Pre-Mortem Before Deciding: Before executing a major financial or life move, assume you are three years in the future and the decision was an absolute disaster. Write down why it failed. Framing the outcome as a guaranteed failure tricks your brain into hunting for vulnerabilities instead of defending its optimism.
   
   
2. Set Invalidation Triggers Upfront: Confirmation bias thrives in ambiguity. Write down the exact conditions that would prove your thesis wrong at its inception, when your objectivity is highest. (e.g., "I am wrong about where the S&P 500 is headed if U.S. Corporate Earnings Growth goes negative year-over-year in the next two quarters"). 
   
   
3. Seek Intelligent Dissent (Red Teaming): Force yourself to read the most articulate, well-reasoned counter case against your position before allocating time or money. If you cannot explain the opposing view well enough that a skeptic agrees with your summary, you don't fully understand the risks of your own position.
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4. Separate Identity from Your Hypotheses: Avoid labeling yourself ("I am a value investor" or "I am a technology bull" or "I only vote democrat/republican" ). When a belief becomes tied to identity, changing your mind feels like a personal defeat. Treat your beliefs as scientific hypotheses: if incoming data disproves the premise, updating your view is good practice, not a loss of face.

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Conclusion

Few of us will face a decision with the same stakes that French Military Command did at the onset of World War II. But the mental trap that brought down France is the exact same one we face every day, especially in the age of social media.

The next time you find yourself holding a conviction so strong that you feel you couldn’t possibly be wrong, that is precisely the moment you need to analyze your confirmation bias.


More Reading:
1 Year of The New Diligence: Choosing Quality in an AI-Led World
Why Gas Prices Rule the Inflation Narrative
How Anyone from Poor to Rich Can Use Money to Buy Happiness
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References

1. Ernest R. May, Strange Victory: Hitler's Conquest of France (New York: Hill and Wang, 2000).
2. Julian Jackson, The Fall of France: The Nazi Invasion of 1940 (Oxford: Oxford University Press, 2003).
3. Karl-Heinz Frieser with John T. Greenwood, The Blitzkrieg Legend: The 1940 Campaign in the West (Annapolis, MD: Naval Institute Press, 2005).
4. Raymond S. Nickerson, "Confirmation Bias: A Ubiquitous Phenomenon in Many Guises," Review of General Psychology 2, no. 2 (1998): 175–220.
5. Daniel Kahneman, Thinking, Fast and Slow (New York: Farrar, Straus and Giroux, 2011).
6. William Hart et al., "Feeling Validated Versus Being Correct: A Meta-Analysis of Selective Exposure to Information," Psychological Bulletin 135, no. 4 (2009): 555–588.
7. Charles G. Lord, Lee Ross, and Mark R. Lepper, "Biased Assimilation and Attitude Polarization: The Effects of Prior Theories on Subsequently Considered Evidence," Journal of Personality and Social Psychology 37, no. 11 (1979): 2098–2109.
8. Mara Mather, Eldar Shafir, and Marcia K. Johnson, "Misremembrance of Options Past: Source Monitoring and Choice," Psychological Science 11, no. 2 (2000): 132–138.
9. Keith E. Stanovich, Richard F. West, and Maggie E. Toplak, "Myside Bias, Rational Thinking, and Intelligence," Current Directions in Psychological Science 22, no. 4 (2013): 259–264.
10. Dan M. Kahan et al., "Motivated Numeracy and Enlightened Self-Government," Behavioural Public Policy 1, no. 1 (2017): 54–86.
11. Charles S. Taber and Milton Lodge, "Motivated Skepticism in the Evaluation of Political Beliefs," American Journal of Political Science 50, no. 3 (2006): 755–769.
12. Don A. Moore and Paul J. Healy, "The Trouble with Overconfidence," Psychological Review 115, no. 2 (2008): 502–517.
13. Barry M. Staw, "Knee-Deep in the Big Muddy: A Study of Escalating Commitment to a Chosen Course of Action," Organizational Behavior and Human Performance 16, no. 1 (1976): 27–44.