"Everything is obvious once you know the answer"

Reading this Freakonomics post, I was struck by its similarities to what Leonard Mlodinow had to say last week at the IdeaFestival. In a world where complexities demand more than a simple - and often wrong - answer, what should we make of "common sense?"

There is hard won information about the practicalities of carpentry and building cabinets, of course, but when it comes to making judgements about climate change, to use another example, conclusions based on the material at hand, from a glance at the local weather, can't hope to say much of anything that is true about the bigger reality because the bigger reality is so much more complex.

Duncan Watts, the author of "Everything You Know is Obvious, Once You Know the Answer:"

Why is the Mona Lisa the most famous painting in the world?  Why did J.K. Rowling‘s Harry Potter books sell over 300 million copies?  And why is Madonna the most successful female musical artist of all time? Now that we know who these superstars are, their success seems easy to explain—common sense even. They simply outperformed the competition. Whether they did that through pure genius, clever marketing, or sheer tenacity is a matter of debate (you be the judge), but in the end, it doesn’t really matter.  In the competitive marketplace of ideas, a product succeeds because it represents what people want—otherwise, they wouldn’t have devoted their scarce time, money, and attention to it. Right?

Well, sort of....

Common sense... is extremely good at making the world seem sensible, quickly classifying believable information as old news, rejecting explanations that don’t coincide with experience, and ignoring counterfactuals. Viewed this way, common sense starts to seem less like a way to understand the world, than a way to survive without having to understand it.

That may have been a perfectly fine design for most of evolutionary history, where humans lived in small groups and could safely ignore most of what was going on in the world. But increasingly the problems of the modern world—distributions of wealth, sustainable development, public health—require us to understand cause and effect in complex systems, with consequences unfolding over years or decades. And for these kinds of problems, there’s no reason to believe that common sense is much of a guide at all.