Behavioral economist, Dan Ariely’s delightful first book, Predictably Irrational, heaps yet one more shovel of dirt onto the fresh but deep grave of traditional, rationalist assumptions about human behavior. The book is a simple, personal, easy-to-read account of Ariely’s research conducted over the past 15 or so years. This research was conducted at his various host universities; all of them paragons of ivy-covered scientific rigor, including MIT, Stanford, The University of Virginia, and The University of California at Berkeley.

The clear and inevitable conclusion of his dozens of research papers summarized in this book is simple: humans don’t make rational decisions. What’s more, the irrationality of their choices isn’t random, but can be predicted and measured. While many of the experiments deal with choices regarding cash, several of them cleverly divorce themselves from money to clearly demonstrate that the goofy human behavior is human-related, not cash-related.

He identifies several predictable forces that act upon humans during decision making, causing them to make irrational choices. These include the distorting effect of similar, but slightly inferior, products offered for sale; the distorting effect of simply thinking about numbers; the distorting effect of items offered for free; the distorting effect of sexual arousal; social norms, ownership, procrastination, self-control, clinging to options, expectations, and being observed.One of the most fascinating experiments he relates proves the existence of what he calls the “decoy effect” showing how people make choices based on relative comparisons rather than on absolute values.

In this experiment, he manages to gather anonymous photos of two of the most attractive young men (as rated by their female peers) on a big campus. Ariely nicknames them George Clooney and Brad Pitt. Then, showing George and Brad to young women, asks their preferences. Of course, their choices are truly random and are neatly divided, fifty-fifty.

He then takes the image of George and slightly doctors it in PhotoShop. By slightly bending his nose and tweaking his brow, Ariely creates a new “George-minus”, the decoy; looking very much like the real George, just not as handsome.

Now he presents three images to a fresh batch of female subjects: George, George-minus, and Brad. In each iteration of this experiment the women chose George 75 percent of the time. When the same experiment included a modified Brad Pitt (Brad-minus), 75 percent of the women chose Brad.

Now, this decoy effect actually makes sense to my rational mind, and I can excuse silly humans for such irrational behavior, but some of the experiments boggle my sense of rational self-respect. Ariely proves that he can make a person pay more for something simply by having them think about bigger numbers beforehand!

It’s easy to admire Ariely’s deft hand in designing these experiments to eliminate spurious effects, revealing only the pure, statistically damning truth about how humans make decisions. And the delicious icing on the cake is that his test subjects are largely composed of the students and faculty of our most intellectually choosy academies; that is, the smartest and most rational people in the world.

Computer programmers are very rational people. They work in a world of dispassionate, brutally honest logic imposed on them by digital computers. It is not surprising that programmers often imagine that their entire world is equally rational. When programmers write software that interacts with other software or other programmers, such an assumption is adequate. But when programmers write software that interacts with normal humans, that assumption generates all sorts of problems.

One problem is the programmer’s assumption that when humans interact with software, they bring similar skills, knowledge, and mental models to the event as the programmer himself. Another problem emerges when the programmer asks the human user how he or she would like the program to be designed. Not only is the human utterly unskilled in designing complex software behavior, their evaluation of their own actions, expectations, and reactions isn’t rational. As Ariely proves, we simply aren’t aware of the forces at work on our decision-making processes.

One of the emergent notions in programming today is the idea that interviewing users and putting in writing their “user stories” is an effective way to determine the form and behavior of the software. While the idea seems rational enough, it simply doesn’t work very well in practice. Users are not sufficiently self-aware, and programmers are not inclined to untangle the complexities of distortions in human perception to make this work. The only successful way to create such user stories is to observe and interview those users to determine their fundamental motivations, and then to synthesize behavioral solutions from first principles. This is the primary skill of interaction designers, and one that is shared by few programmers, and fewer users.

Ariely’s work joins the growing canon of behavioral research that is putting the lie to the long-unquestioned assumptions Western secular humanists have been making about human cognition and behavior. It’s about time.