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Scams, Myths & Reality Check · Beginner · 5 min

Survivorship bias in success stories

You can explain survivorship bias, show with a coin-flip example how luck creates 'geniuses', and spot it in success stories and fund records.

Only survivors tell stories

The trader who turned 1,000 into a fortune. The student who quit their job after a course. The fund that beat the market for ten years. Every one of these stories is told by someone who made it.

The people who tried the same thing and failed do not make videos, sell courses or appear in rankings. That missing half changes what the stories mean.

Luck makes geniuses

Survivorship bias is the error of drawing conclusions only from the cases that remain visible, the survivors, while the failures have dropped out of sight. Because only winners are shown, a strategy, a course or a type of trading looks more successful than it really is.

A simple thought experiment shows how strong the effect is. Imagine 1,024 people, each flipping a fair coin. Anyone who flips tails drops out.

Steps 1,024 people each flip a coin and drop out on tails. About 512 remain after one flip, 32 after five and one after ten flips, with ten heads in a row purely by chance. 1 1,024 start flipping 2 512 after 1 flip 3 32 after 5 flips 4 1 'genius' after 10

That person did nothing special. The chance of ten heads in a row is 1 in 1,024, so among 1,024 people one such streak is expected. But from the outside, ten correct calls in a row look like skill. If that person now explains their "method", most viewers will never think about the 1,023 who flipped the same coin.

Markets work similarly. With millions of people trading, some impressive records will appear by luck alone, and those are the ones that become visible. The SEC warns that social media can make investments look more popular and successful than they are.

The same bias affects data. Researchers studying US mutual funds found that funds disappear mainly after several years of poor performance. When only surviving funds are counted, average performance looks better. The bias was small for one-year samples but about one percentage point a year for samples longer than fifteen years.

Closed funds vanish

A fictional fund family launches 20 trading funds. Ten years later, 8 have closed or been merged into others after poor results. The remaining 12 are shown on the website.

A course that shows ten successful students out of an unknown number works the same way. Without the full count and everyone's results, the success stories say nothing about the odds.

Common mistakes

The takeaway

We see the winners and never the many who failed the same way. With enough people trying, impressive records appear by luck alone.

Check yourself

Quick quiz

4 questions. Instant feedback, nothing is saved.

  1. 1Tap the step that would be shown in a success video.

    Tap the chart.

    Steps Chart for the question: Tap the step that would be shown in a success video. 1 1,024 start flipping 2 512 after 1 flip 3 32 after 5 flips 4 1 'genius' after 10

    The one person with ten heads in a row tells the story. The 1,023 who dropped out are not in the video.

  2. 21,024 people each flip a fair coin ten times. How many would you expect to get ten heads in a row?

    The chance is 1 in 2 to the power of 10, which is 1 in 1,024. Out of 1,024 people, one is expected.

  3. 3Why do fund performance averages that include only funds still alive look better than reality?

    A study of US mutual funds found that funds disappear mainly after years of poor performance, which inflates the averages of survivors.

  4. 4A course shows ten students who became full-time traders. What is the most useful question?

    Without the total and the results of everyone, ten success stories say nothing about the odds.

of 4 correct.

Sources

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