A wise man knows one thing – the limits of his knowledge

by John Kay

Financial Times
November 29, 2011

John Maynard Keynes, who never tried to conceal that he knew more than most people, also knew the limits to his knowledge. He wrote “about these matters – the prospect of a European war, the price of copper 20 years hence – there is no scientific basis on which to form any calculable probability whatever. We simply do not know.”

And Keynes was right. He published these observations in 1921, and 20 years later Britain was engaged in a desperate, and unpredictable, struggle with Germany.

But lesser men find prognostication easier. I have been looking at some of the models people use, in both the public and private sectors to predict events.

The models share a common approach. They pose the question: “How would we make our decision if we had complete knowledge of the world?” With such information you might make a detailed assessment drawing together many different pieces of relevant information on matters such as costs, benefits, and consequences.

But little of this knowledge exists. So you make the missing data up. You assume the future will be like the past, or you extrapolate a trend. Whatever you do, no cell on the spreadsheet may be left unfilled. If necessary, you put a finger in the air.

More