Dan Ariely is a behavioural economist. In this TED talk he presents his experiments and insights into predictable irrationality. Surprising or not, there are many cases of irrational behaviour in humans. Here Ariely focussed on intuitions and cheating which he and his lab investigated. Let me summarise what he has to say about cheating. The experiment his lab conducted is quite simple: a group of participants receives a sheet of paper with N number of mathematical tasks to solve. After a certain time, which is chosen so that it is impossible to solve all tasks, the students have to hand back their sheets. They get paid for every solved task. Ariely explains how they then added possibilities to cheat, for example, students would shred their sheets and should then tell how many tasks they solved. Interestingly, the students would cheat a little but not overly much. This is a pattern that is consistent with several modifications of the experiment that would in theory allow to cheat more. However, a specific version of the experiment (students would ask for tokens instead of money and could then exchange the tokens with money somewhere else) drastically increased cheating. Separating the lie and receiving the reward (money) as well as abstracting money for tokens made cheating more tempting. And finally, Ariely explains a version of the model where an acting student bluntly cheated; after 30s in to the experiment the actor would say that he/she finished the task and received its reward. As this obvious act of cheating wasn’t punished, one could expect that it increases cheating. But this was not always the case. It depended on the sweatshirt of the acting student. When the shirt had the logo of the university all other students were studying at, cheating would indeed go up, while there was no cheating when the shirt was from a different university. People seem to either want to separate themselves from misbehaving individuals, or to identify with a group of people and their behaviour. This has important implications for what we have seen and still see at stock markets.