One of the less endearing characteristics of human behaviour is to take the credit when things go right, and blame someone else when they go wrong. On which basis, bank chief executives felt wonderfully empowered when product sales fuelled by derivatives and leverage soared in the credit boom.

In a recent note, Michael Mauboussin of Legg Mason wrote: "It is well within human nature to assume that the flow of profits equals insight into the market's workings. This creates a sense of shock when events occur outside the predictions of the market."