In his book Actual Minds, Possible Worlds, the psychologist Jerome Bruner tells the story of a colleague who did a simple but interesting study. He took a list of twelve standard personality traits with positive and negative poles (such as lazy and energetic, honest and dishonest) and threw them together into random combinations of negatives and positives on a series of cards. He presented each card to a subject and asked them for a general description of the person depicted by those traits. Surprisingly the task was completed easily, every time, no matter how unlikely the combinations. No one ever said “It can't be done, there's no such person”. Not once did these random combinations of characteristics elicit bafflement or hesitation on the part of the subjects. Bruner concluded (in the gendered language of his time) that with this “staggering gift for creating hypotheses … Man … is infinitely capable of belief. Surprising that he has not been described as Homo Credens” (1986: 51).

If we are infinitely capable of belief it is little surprise to see a correlative human vulnerability to deception and self-deception. If you lock too readily on to a way of seeing, a good description or a satisfying explanation you can easily be fooled. And we fool ourselves equally easily. According to recent research we assume we are quite a lot smarter, better looking and nicer than others think we are (and that's without alcohol).