I realized I had a problem while standing in the cereal aisle of the supermarket. My wife was in the express checkout line, waiting for me to return with a box of Cheerios. This might sound like a simple task — "Just get the kind you want," she said — but what kind did I want? Was I in the mood for plain old Cheerios? Or did I crave the sweetness of Honey Nut? On the other hand, I'd never tried the Apple Cinnamon or Multigrain varieties: maybe I was missing something delicious? I stared in existential despair at the multitude of boxes. General Mills was ruining my life.
My mishap in the cereal aisle — it took me several minutes before I settled on Honey Nut — taught me something important: I didn't know how to use my brain. I might think too much about breakfast, but there were other moments when I would think too little, and end up with an impulsively purchased sweater or a $4 latte I didn't really want. In other words, it was my own frailties that first got me interested in the science of decision-making.
What did I learn? One of the most surprising things has been just how limited the mind is, at least when it comes to everyday decisions like picking a cereal or exerting self-control. (I thought I'd get the bad news out of the way first.) As I write in the book, we're like an incredibly complex computer operating system — e.g., Windows Vista — that was rushed to market. As a result, our software is full of bugs that evolution has yet to resolve.
Consider this experiment. You're sitting in a bare room, with just a table and a chair. A scientist in a white lab coat walks in and says that he's conducting a study of long-term memory. (He's lying: this is actually a study of self-control.) The scientist gives you a seven-digit number to remember, and asks you to walk down the hall to the room where your memory will be tested. On the way to the testing room, you pass by a refreshment table for subjects taking part in the experiment. You are given a choice between a decadent slice of German chocolate cake or a bowl of fruit salad. What do you choose?
Now let's replay the experiment. You are sitting in the same room. The same scientist gives you the same dishonest explanation. The only difference is that instead of being asked to remember a seven-digit number, you are only given two numbers, a far easier mental task. You then walk down the hall, and are given the same choice between cake and fruit.
You probably don't think the number of digits will affect your choice. If you choose the chocolate cake, it is because you want cake. But you'd be wrong.
When the results from the two different memory groups were tallied up, the scientists observed a striking shift in behavior. Fifty-nine percent of people trying to remember seven digits chose the cake, compared to only 37 percent of the two-digit subjects. Distracting the brain with a challenging memory task made people much more likely to give in to temptation, so that they chose the calorically-dense dessert. (German chocolate cake is to adults what a marshmallow is to four-year-olds.) Their self-control was overwhelmed by five extra numbers.
Why did the two groups behave so differently? According to the Stanford scientists who designed the experiment, the effort required to memorize seven digits drew cognitive resources away from the part of the brain that normally controls our emotional urges, which are telling us to eat cake. Because working memory and self-control share a common cortical source — the prefrontal cortex — a mind trying to remember lots of information is less able to exert control over its impulses. The substrate of reason is so limited that a few extra digits can become an extreme handicap.
I think a similar thing was happening when I was trying to pick a cereal. There were just too many varieties and too many brands — the typical supermarket has more than 300 cereal options — and so my feeble, Paleolithic brain was overwhelmed. That, at least, is what I told my wife.