Gary Klein is the intellectual leader of students of Naturalistic Decision Making (NDM), who study real people in natural situations. He rejects the focus on biases in heuristics, doing artificial experiments and is highly skeptical about choosing algorithms over human judgments. Klein is known for studies of expertise in firefighters and the development of intuitive skills in experienced experts. Despite their differences, Kahneman worked together with Gary Klein on a joint project in order to answer the question “When can you trust an experienced professional who claims to have an intuition?” They both agreed about Gladwell’s bestselling book ‘Blink’ about art experts that had the gut feeling that the object was a fake, but could not tell what it exactly was that made them think it was not the real deal. They knew it was a fake without knowing how they knew: a perfect example of intuition.

While Kahneman’s views of intuition were shaped by observing the illusion of validity in himself and reading Meehl’s review about clinical predictions, Klein’s thinking was shaped by his studies of fire ground commanders. He observed and interviewed them. He introduced the ‘recognition-primed decision (RPD) model, which applies to several experts (from fire commanders to chess masters). System 1 and System 2 are both involved in this process. A tentative plan automatically comes to mind (System 1) and then gets mentally tested (System 2). The model of making intuitive decisions involves recognition: the situation provides a cue, the cue retrieves information from memory, which provides the solution. Intuition is merely recognition.

Information gets stored in memory by learning emotions, like fear. A scary experience stays with you for a long time. Fear can be learned by experience and by words. Soldiers get trained to identify situations and firefighters discussed all types of fires with others. Emotional learning is quick, developing expertise takes a long time. Chess masters need more than 10.000 hours of practice to reach the top. During these hours, players become familiar with all the possible moves and able to quickly read the situation.

Kahneman and Klein agreed that the confidence of people in their intuitions is not a reliable source of validity. But if subjective confidence cannot be trusted, how do we know when judgments reflect true expertise? The answer lies in the two conditions for acquiring a skill:

• The environment must be sufficiently regular so its predictable

• There must be an opportunity to learn the regularities through prolonged practice.

An intuition is normally skilled when both conditions are met. Chess players, nurses, physicians, firefighters and sportsmen are active in regular, orderly situations. Political scientists and stock pickers are not, they operate in a less regular (non-validity) environment.