Introduce the following ingredients in a bowl and stir delicately during several years:

The quality of the ingredients is essential to the success of any recipe. As outlined by the previous examples, we are all following the same recipe but using ingredients from very diverse origins. It’s not surprising that we all get a different result.

Common sense results from a lifetime learning from everyday situations. For my 1-year old toddler, going down headfirst from the couch was common sense until recently. Common sense is not inborn. It’s developed over time. The right to bear arms was common sense when the Constitution of the United States was written, but this right is more and more contested among US citizens, which proves common sense is not set in stone and is certainly not as common as we think. Ask voters during an election if their ballot follows common sense, and they will all answer affirmatively. Common sense is not common.

We must therefore learn to consider common sense as our uncommon sense. Cannibalism still makes sense in some cultures or in different times and places. It’s not a problem as long as you plan your next vacation wisely.

Common sense is maybe not common, but it is still useful. We use our common sense thousands of times every day. When commuting, our common sense keeps us safe, by not crossing the roads in front of a car, or by avoiding eye contact in the subway. Common sense is reliable for these small, automatic decisions, but common sense is a liability for meaningful, challenging decisions.

Criticizing common sense is tricky. It is widely regarded as a good thing. But as we have discussed, common sense is not as common as most people imagine. If using our common sense to reason about how we behave is "acceptable," using it to reason about others is definitively wrong.

To illustrate the limits of common sense, we must go back in time to the beginning of the Scientific Revolution. In 1514, Nicholas Copernicus discovered that the Earth orbits around the sun. Claiming that the Earth was not at the center of the Universe if you are a Polish priest was asking for trouble, and thus Copernicus published his landmark discovery anonymously…​ We will have to wait almost a century for two astronomers, Johannes Kepler and Galileo Galilei, to validate his theory. Common sense is stubborn.

This example illustrates that common sense changes over time, which means relying on common sense cannot guarantee you to be right in the future. What else that we believe to be self-evident now will seem wrong to us in the future? Why is common sense so wrong?

The truth is common sense excels at filling the blanks to pretend things have sense. In Everything Is Obvious, sociology researcher Duncan J. Watts mentions: "Common sense is wonderful at making sense of the world, but not necessarily at understanding it."^[2] As we have seen in the previous section, common sense is uncommon, or personal. Common sense is therefore subject to our numerous cognitive biases. For example, the attentional bias makes us pay more attention to certain stimuli and ignore the vast majority of available information. And by ignoring details, we often miss what is really making sense.

But common sense is not just wrong, it is sometimes contradictory. We say that birds of a feather flock together but also that opposites attract. "When opposite ideas appear equally obvious, something must be wrong with the entire concept of obviousness," adds Duncan J. Watts in the same book. Similarly, we can quote the Complementary Law: "Any two points of view are complementary." Even global warming can make sense for a country like Russian to turn Siberia into the breadbasket of the world and the Arctic sea the crossroad of the world as higher temperature means more favorable conditions for agriculture and new maritime navigation lines at the North pole.^[3]

What is obvious is that common sense is of little help in decision making. And when common sense fails us, we often ask for more common sense as if we didn’t rely on it initially and as if it could make a difference…​ We need a better approach.

Relying less on common sense is hard. Using common sense feels natural, a lot more than relying on our intuition, although both are the same thing. If you doubt your intuition, you must doubt common sense too.

We have already elaborated that we cannot trust our common sense. We don’t think the way we think we think.^[4] We are not rational creatures, even if we think we are. The seminal book Thinking, Fast and Slow condenses in more than 400 pages the most surprising experiments about our irrationality. We can’t use common sense to make rational decisions.

The solution is instead to rely more on science ^[5], and adopt a more systematic approach, especially at work. We need what professor Jim Taylor called "reasoned sense," that is, sound judgment based on rigorous study of an issue.^[6]

Common sense is the land of misinformation. We need to look for facts. We need to read more books. We need to be better informed to make better decisions. We need to learn.

In the end, common sense makes sense until you have thought critically about it, in which case, common sense stops making sense. Learning is the antidote. Here is a better definition of common sense that I have found online:

I want to conclude this article with my chocolate bar that makes sense. What the company says, in the end, is that they tried to do what is best for every actor in the process. Doing his best to create a positive impact in our world is, for sure, a great example of something that makes sense. Saying it is great. Doing it is better. Just make sure not to use your common sense to make sense 😉.