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[6] The False Prophet of Common Sense

Why it’s easy to be overconfident in our intuitions

Every fall semester since I arrived at UC Berkeley, I have taught the introductory class on leadership to incoming MBA students at the Haas School of Business. I begin the first day by acknowledging that most of the students already know a lot about leadership. In fact, some wonder why they have to take the class at all because so much of what they believe about leadership in organizations seems like obvious common sense. I acknowledge these concerns and note that many of the class's most important themes build on common-sense conclusions, such as:

• Happy workers are productive workers
• Smart managers evaluate people based on results
• Interviews are the best tools for selecting employees
• Cohesion increases the performance of teams and organizations
• Bureaucracies, rules, and red tape impede organizational efficiency

I then inform the students that research has found all of these claims to be wrong, or at least found important instances in which they do not hold true. Part of why the class is so fun to teach is that it gives me the opportunity to correct my students' flawed common sense by shining the bright light of evidence into the dark gaps of their erroneous beliefs.

Many false beliefs survive because we never manage to collect the evidence necessary to test them. And there are many things for which common sense presents a compelling explanation that is just plain wrong. For example, when the germ theory of disease was first proposed by Girolamo Fracastoro in 1546, it was dismissed as implausible. Who would believe that things so minuscule could have such momentous effects? Evil spirits seemed a more plausible explanation for disease. Indeed, when the bubonic plague was sweeping through Europe in the 14th century, people suspected cats, whose secretive ways seemed to imply magical powers, and perhaps even demonic agency. In an attempt to banish the evil spirits infecting them, Europeans killed cats in large numbers. In fact, it was rats and the fleas that inhabited them that were the carriers of the plague. Without the cats to keep the rats under control, the plague ran rampant.

Pope Clement VI issued a papal edict in 1348 in which he called the plague a "pestilence with which God is affecting the Christian people." The European physicians offered common-sense advice on how to avoid it: avoid exercise and bathing; wear religious talismans; burn incense and carry flowers; smell strong odors to overcome the plague vapors. It took hundreds of years and the accumulation of overwhelming scientific evidence before the germ theory was generally accepted.

Likewise, the evidence that the earth orbited the sun was once so at odds with common sense that it took a long time to dispel the belief that the opposite was true. Our confidence in ourselves and in the correctness of our opinions is often driven by the sense that what we believe is simply common sense. But in reality, common sense imbues our opinions with a false confidence that can be a powerful impediment to grasping and accepting the truth. Science has cut down common sense again and again as a tool for understanding both the natural and social worlds. Common sense is terrible at predicting important phenomena, such as who will make the better employee, where the stock market is headed, and whether a new product will sell.

Common sense and intuition are not worthless — there are good reasons why they come to us so naturally and feel so right. It is common sense, for instance, that two heads are better than one. That's why we so often seek others' advice and assemble teams to help get things done. But common sense also tells us that too many cooks spoil the broth. Larger teams do not always improve the quality of the output. These important questions cannot be resolved by the simple aphorisms that common sense provides us, but there are answers to them. These answers come from research.

If you care about understanding something, then you need to study it, either learning from others' experience or collecting the data yourself that would allow you to test the causal claim of your common-sense theory. In the absence of data, we are all free to speculate, but it is worth reminding yourself that your speculation is exactly that — a flimsy common-sense story that is vulnerable to being blown over by a gust of actual evidence.

What seems like common sense to us is, to a great extent, driven by intuition. And as authors like Daniel Kahneman, Max Bazerman, Duncan Watts, Richard Thaler, and Cass Sunstein have written about so articulately, intuitive judgment is beset by biases. It is possible to train your intuition to improve its fidelity, but that requires substantial training, practice, and feedback. It is rare that life provides us with sufficient training, practice, and feedback. Without them, it is dangerous to place too much confidence in your common-sense intuitions.