Skip to main content
Cognitive Biases

Placebo Investors

A cognitive bias where success is attributed to skill when it may be due to luck, illustrated by a Monte Carlo simulation showing that random outcomes can produce consistent winners purely by chance.

THE IDEA

Placebo Investors

I have often been faced with questions of the sort: “Who do you think you are to tell me that I might have been plain lucky in my life?” Well, nobody really believes that he or she was lucky. My approach is that, with our Monte Carlo engine, we can manufacture purely random situations. We can do the exact opposite of conventional methods; in place of analyzing real people hunting for attributes we can create artificial ones with precisely known attributes. Thus we can manufacture situations that depend on pure, unadulterated luck, without the shadow of skills or whatever we have called nonluck in Table P.1. In other words, we can man-make pure nobodies to laugh at; they will be by design stripped of any shadow of ability (exactly like a placebo drug).

We saw in Chapter 5 how people may survive owing to traits that momentarily fit the given structure of randomness. Here we take a far simpler situation where we know the structure of randomness; the first such exercise is a finessing of the old popular saying that even a broken clock is right twice a day. We will take it a bit further to show that statistics is a knife that cuts on both sides. Let us use the Monte Carlo generator introduced earlier and construct a population of 10,000 fictional investment managers (the generator is not terribly necessary since we can use a coin, or even do plain algebra, but it is considerably more illustrative—and fun). Assume that they each have a perfectly fair game; each one has a 50% probability of making $10,000 at the end of the year, and a 50% probability of losing $10,000. Let us introduce an additional restriction; once a manager has a single bad year, he is thrown out of the sample, good-bye and have a nice life. Thus we will operate like the legendary speculator George Soros who was said to tell his managers gathered in a room: “Half of you guys will be out by next year” (with an Eastern European accent). Like Soros, we have extremely high standards; we are looking only for managers with an unblemished record. We have no patience for low performers.

The Monte Carlo generator will toss a coin; heads and the manager will make $10,000 over the year, tails and he will lose $10,000. We run it for the first year. At the end of the year, we expect 5,000 managers to be up $10,000 each, and 5,000 to be down $10,000. Now we run the game a second year. Again, we can expect 2,500 managers to be up two years in a row; another year, 1,250; a fourth one, 625; a fifth, 313. We have now, simply in a fair game, 313 managers who made money for five years in a row. Out of pure luck.

Meanwhile if we throw one of these successful traders into the real world we would get very interesting and helpful comments on his remarkable style, his incisive mind, and the influences that helped him achieve such success. Some analysts may attribute his achievement to precise elements among his childhood experiences. His biographer will dwell on the wonderful role models provided by his parents; we would be supplied with black-and-white pictures in the middle of the book of a great mind in the making. And the following year, should he stop outperforming (recall that his odds of having a good year have stayed at 50%) they would start laying blame, finding fault with the relaxation in his work ethics, or his dissipated lifestyle. They will find something he did before when he was successful that he has subsequently stopped doing, and attribute his failure to that. The truth will be, however, that he simply ran out of luck.

When to use it

  • Evaluating the track record of investment managers or financial advisors.

  • Assessing the success of business strategies that may have benefited from market timing.

  • Interpreting personal achievements in competitive fields with high randomness.

  • Designing experiments or simulations to test the role of luck in performance outcomes.

FROM THEORY TO EVERYDAY LIFE

In practice

01

Monte Carlo Simulation of Investment Managers

A population of 10,000 fictional investment managers each have a 50% chance of gaining or losing $10,000 per year. Managers with a single losing year are fired. After five years, purely by chance, 313 managers have a perfect record of five winning years. Luck alone can create the appearance of skill.

02

Real-World Attribution of Success

A successful trader with a lucky streak is celebrated for his style, incisive mind, and childhood influences. When his performance declines, the same analysts blame his work ethic or lifestyle, ignoring the possibility that he simply ran out of luck.

✳

A MOMENT TO REFLECT

Put it to work.

  1. How can you distinguish between luck and skill when evaluating your own successes?

  2. What are the dangers of attributing long-term success to personal qualities without considering randomness?

  3. How does survivorship bias affect the way we judge investment managers or entrepreneurs?

CONTINUE THE CONVERSATION

Source texts

  • Fooled by Randomness The Hidden Role of Chance in the Markets and in Life (Nassim Nicholas Taleb)
← More cognitive biases