Confirmation bias is the tendency to search for, interpret, and favor information that confirms existing beliefs while discounting contradictory evidence. In investing, it manifests as selectively reading bullish analysis on stocks you own and ignoring bear cases.
The Investment Trap
You buy a stock because you believe the company is undervalued. Now you're embedded in confirmation bias. You read earnings calls looking for positives. You dismiss analyst downgrades as "wrong." You attribute stock declines to temporary market noise rather than reconsidering your thesis.
Your conviction in the investment strengthens over time not because evidence supports it, but because you've selectively exposed yourself to confirming evidence and filtered out contradictions.
How It Destroys Returns
Confirmation bias causes good investment theses to survive longer than they should and bad ones to persist indefinitely. A company might be fundamentally deteriorating, but if you've committed to owning it, confirmation bias will find reasons to hold: "the market doesn't understand," "competition will prove manageable," "management will turn it around."
Structural Defense
The antidote is structural: explicitly seek contrary perspectives. Before adding to a position, read the bear case. Before conviction solidifies, talk to someone who disagrees. A simple rule: "Before holding a position 1+ year, I read a bear case from someone credible."
This forces engagement with contradictions, preventing confirmation bias from completely filtering your information diet.
