The Drunkard’s Walk by Leonard Mlodinow

Mlodinow, Leonard. The Drunkard’s Walk: How Randomness Rules Our Lives. 2008. New York: Vintage, 2009.

We are bad judges of probability. When we get beyond the most simple probabilities, our intuition is terrible. It requires a rigorous logic that can trip up even professionals we might expect to know better. It can lead us to make inappropriate judgments about others and ourselves.

That is the premise presented by Leonard Mlodinow in The Drunkard’s Walk. The title refers to a random path that describes many things in nature, like Brownian motion, and society, like the stock market.

Mlodinow describes several way how and reasons why we make false assessments of probability. To begin with, we simply have poor intuition about randomness. Our brains are biased to see patterns even if one isn’t truly there. We can look into the past and piece together how we got where we are, ignoring all the ambiguities we faced at the time, but we can’t easily identify clear marker for the future. We make value judgments based on results when the results are due as much or more to random events as to the efforts of people. Worse, we make value judgments about people even when we know a result related to them is random. With each of these problems, the author presents examples from history or scientific studies.

In contrast to these problems, Mlodinow presents the sometimes counterintuitive, but more correct, views that come from using logic and statistical inference. In this manner her present several concepts of probability and statistics such as regression to the mean, the law of large numbers, Bayesian analysis, the law of errors, and normal accident theory. This isn’t a textbook, though, so the descriptions are aimed at making people aware of the power of these methods for correcting false intuitions, not training future statisticians.

In addition to these things, the book is a history of probability and statistics. Mlodinow goes back to the people who invented, developed and popularized the knowledge he is presenting. Many of these people are unusual characters. For instance, he introduces the battling Bernoullis, a family of mathematicians I was first introduced to through my background in hydraulics, who are colorful and combative enough to make an interesting subject by himself or herself. We get to meet some interesting gamblers, too.

Throughout the book, Mlodinow is building to the argument he presents in the final chapter. Namely, we should not judge people mainly by their results, whether or not they are successful or have failed, are rich or poor, are at the top or at the bottom. People with little difference in ability can have great differences in success due to random factors. We shouldn’t put too much stock in those that success or be to harsh with those who don’t.

We should take courage for ourselves, too. The more attempts we make, the more likely we are to eventually have a success.


If you’re interested in this book, you may also be interested in
Chance by Amir Aczel
The Numbers Game by Michael Blastland & Andrew Dilnot
The Pinball Effect by James Burke
The Unfinished Game by Keith Devlin
War Against the Weak by Edwin Black