I experience this every day. I sit at the table with people that have neither studied nor have any experience in dietary medicine and I hear them state with certainty "I don't eat any carbohydrates, because they make you fat," "I don't eat any meat, because it clogs up the vessels," "I currently do intermittent fasting, in order to increase my metabolism," and so on. When I listen to them, the only thing I wonder about is where this certainty comes from. How are they so certain that carbohydrates make you fat? Who has confirmed that meat clogs up the vessels? Why are they so certain about issues that the dietary science is not sure about? This is the Dunning–Kruger effect, a cognitive fallacy that makes us believe with certainty things about which we wouldn't be so sure if we knew more about them. In 1999, Dunning and Kruger, the famous duo of psychologists, published a really important study that described the effect that was named after them. The study was carried out as follows. They asked some people to take part in some tests, and then they asked them to estimate their results compared to the average. What they found out was that the less competent participants, the results of whom were 12% on average, believed that their results were 62%. If the average was 10 out of 20, the participants that got 2.4 out of 20 would believe that they got 13 out of 20. The researchers described this fallacy as an inability of the brain to know that it doesn't know. The Dunning–Kruger effect is described really nicely with a curve that shows our knowledge about a subject and the certainty we feel regarding how well we know it. Let's say that someone knows nothing about diet. They have no knowledge about this subject and they're certain that they don't know. For some reason, they decide to go online to find out some things about diet. Their knowledge soon starts to increase, but their self-confidence increases much faster than their knowledge. They soon have very high self-confidence and certainty about what they know, and they often become an evangelist of diet. They start teaching their knowledge to everyone with great certainty. Socrates said "The only thing I know is that I don't know." But for the people at this point on the curve, the exact opposite is true. They're certain that they know. They often become evangelists of what they believe is a healthy diet and preach it to everyone passionately. In fact, they often wonder why, although we've studied for many years and we've dedicated our professional life to this scientific subject, we don't clearly see what they teach. When we tactfully disagree with what they say, they often believe that we haven't studied well enough or even that we are paid by the others, the evil ones, namely the ones that passionately evangelize the opposite. However, if they insist, if they start reading more, or even better, if they have to help people that trust them for guidance, they start realizing that what they passionately believe doesn't work for everyone. For a 25-year-old man that exercises, quitting carbohydrates may suffice to have a body worth posting on Instagram, but when a 50-year-old woman in menopause asks for guidance, they realize that what they recommend makes her fat, instead of helping her lose weight. At that point, if they're ridiculous, they'll attack the poor client, accusing her of lying, of not following the instructions properly, and so on. But if they're not that ridiculous, they may enter the second phase and realize that their knowledge is very little and feel desperate. If they endure the initial disappointments and continue studying and applying their knowledge, they may reach the third phase after many years, where they know enough things to be able to help without being absolutely certain about what they recommend. This is the point where we approach the subject with curiosity and excitement, where our failures don't cause disappointment, but open a new field of knowledge and experience. As the famous F1 driver, Niki Lauda, said, "Wins never taught me anything. It was only the defeats that made me a better driver." When someone gives us a piece of advice, how can we understand if they know what they're talking about or not? Since certainty and self-confidence can't help us understand if someone knows a subject well or not, is there any other way to understand if the person talking or what they're saying comes from true, deep knowledge? There are two ways. The first one is to check if the person talking has degrees and experience related to the subject they're talking about. If someone has studied the subject they're talking about in depth and daily work on it acquiring the necessary experience, then what they're saying is probably right. However, in some cases, people that have degrees are clueless, while there are people with no degrees that have deep knowledge in a subject, because they've done significant research on their own. What can you do in that case? Pay attention to the way they're speaking. If you often hear words indicating modesty, humbleness and lack of certainty, such as "perhaps", "maybe", "often", "usually", "in most cases", "I think", "it seems", and similar phrases, the person talking is very likely to be knowledgeable. On the contrary, if you hear dogmatic phrases indicating certainty and self-confidence, such as "certainly", "always", "definitely", "never", "no way", "not a chance", "I'm absolutely certain", the person saying these is very likely to know so little that they're not to be trusted for this subject. If you'd like to see my course in the Dunning-Kruger effect, you have to watch the video on my right. Thank you very much!