Fooled by Randomness

Fooled by Randomness

Nassim Nicholas Taleb

Proxy Trap

Metrics become mirages when optimized directly.

A rational person would act accordingly in the selection of strategies, and set his emotions in accordance with his results. Yet I have experienced leaps of joy over results that I knew were mere noise, and bouts of unhappiness over results that did not carry the slightest degree of statistical significance.
False Positives

Rare signals drown in false positives.

As a rational trader (all traders boast so) I believe, as I discussed before, that there is a difference between noise and signal, and that noise needs to be ignored while a signal needs to be taken seriously. I use elementary (but robust) methods that allow me to calculate the expected noise and signal composition of any fluctuation in my trading performance. For example, after registering a profit of $100,000 on a given strategy, I may assign a 2% probability to the hypothesis of the strategy being profitable and 98% probability to the hypothesis that the performance may be the result of mere noise. A gain of $1 million on the other hand, certifies that the strategy is a profitable one, with a 99% probability. A rational person would act accordingly in the selection of strategies, and set his emotions in accordance with his results. Yet I have experienced leaps of joy over results that I knew were mere noise, and bouts of unhappiness over results that did not carry the slightest degree of statistical significance.
Desperate Pivots

Desperation, not genius, drove transformative pivots.

Things are always obvious after the fact. ... When you look at the past, the past will always be deterministic, since only one single observation took place. ... While we know that history flows forward, it is difficult to realize that we envision it backward.