Self-Attribution Bias — Success Is My Skill, Failure Is Someone Else's Fault
When you make a profit, 'my sharp eye, of course'; when you take a loss, 'the market went crazy.' Sound familiar? This convenient interpretation blocks you from getting better.
What Self-Attribution Bias Is
Self-attribution bias is the tendency to attribute good outcomes to your own ability and effort, and bad outcomes to luck or external circumstances. It is also called self-serving bias.
This bias is a defense mechanism that protects self-esteem, but it prevents you from learning properly from outcomes. In success you miss the role of luck, and in failure you miss your own mistakes.
Why It's Dangerous: Fuel for Overconfidence
Self-attribution bias is core fuel that grows overconfidence.
When a stock you bought in a bull market rises — even though the whole market actually lifted it — you remember it as 'my skill.' As these success experiences pile up, the conviction that 'I can read the market' grows, and you increase your trading frequency and bet sizes.
Conversely, since you dismiss losses as 'due to external bad news,' you repeat the same mistakes. Research also identifies self-attribution, the illusion of control, and optimism as components of overconfidence, which can lead to excessive risk-taking such as executives pursuing reckless mergers and acquisitions.
How to Separate Skill from Luck
The key is to record the 'process,' not the outcome.
An investment journal in which you write down 'why you made this decision' in advance of every trade is powerful. Comparing it with the outcome later lets you distinguish a good judgment that had bad luck from a bad judgment that had good luck.
You must also compare your return against a market index (benchmark). If the market rose 30% and you earned 20%, that may not be 'skill' but a result that fell short even with the market's help. The habit of comparing multiple assets against the same standard strips away the illusion of self-attribution.
よくある質問
Q. How is self-attribution bias different from hindsight bias?
Self-attribution bias distributes the 'causes of an outcome' in your favor (success = me, failure = others), while hindsight bias distorts memory after the fact into 'I knew it all along.' Both share the trait of blocking you from learning accurately from the past.
Q. How exactly should I keep an investment journal?
At the moment of buying or selling, write down in advance ① the reason (basis) for the decision, ② the scenario you expected, and ③ the condition under which you'd admit you were wrong. Comparing this with the outcome later lets you separate skill from luck, and lets you learn from factual records instead of memory distorted by self-attribution bias.
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