The mistaken idea that reason and emotion are separate. A lot of scientists still believe in reason and it really screws up their thinking because they confuse their rationalizations for reasoning without reflecting to see whether the underlying feeling makes sense. All human thinking–including mine–is constantly colored and distorted by our emotions. Unless you’re hyperaware of that, then you don’t watch your emotions and correct accordingly so that over the long run you can tease out a better version of reality. The idea of reason lets you think that the effects of emotion are a temporary state. They’re a permanent and constant one. If you’ve listened to that episode, then you know Jon Haidt’s analogy of the brain being like a rider and an elephant. There’s no point at which the rider gets off the elephant and simply goes for a walk around without the elephant. They are inextricably linked in your brain. You can purchase the book Descartes’s Error: Emotion, Reason and the Human Brain by Anthony Demasio