It was a day nobody on Wall Street would ever forget. On 9 September 2008, Lehman Brothers - one of the US's largest and most respected investment banks - filed for bankruptcyApply to be declared bankrupt, so that you do not have to pay all your debts.. The traders hunched over their screens read the news with incredulityDisbelief., as the worst economic recession in modern history roared into life. But one man had seen it coming.

Nassim Nicholas Taleb is an expert on risk and probability, and - having spent 21 years as a trader himself - he was convinced that money managers had been approaching it in the wrong way. His theory is that people put too much faith in the patterns of the past to predict the future, relying on statistics that are erroneousMistaken. or incomplete.

Instead of assuming that something will happen because it generally has before, he argues we should be prepared for rare and random events. His best-known book, The Black Swan, was published a year before the 2008 crash, and takes its title from an old proverb referring to something that cannot exist. The proverb gained currency in Europe because people there had only ever seen white swans - so, when travellers to Australia brought back news of black ones, it was a complete surprise.

Taleb argues that when you invest your money, you should factor in the unexpected. If you put most of your money into safe stocks and a small amount into high-risk ones, you will make more than by putting all of it into medium-risk ones.

His theories are not just financial. "As we travel more on this planet," he wrote in The Black Swan, "epidemics will become more acute. The successful killer will spread vastly more effectively. I see risks of a very strange, acute virus spreading throughout the planet."

The authorities in Singapore were so struck by this that they asked Taleb to help them devise a strategy for such an epidemic. As a result, Singapore has had just over 300 cases of Covid-19 reported in two months, while other countries have had thousands.

Taleb even applies his theory to exercise. He recommends that instead of following a moderate regime, you should mix gentle exercise with occasional violent exertion - mirroring the life our primitive ancestors lived in their highly unstable environment.

Some say that Taleb is clearly brilliant at what he does: one of the companies he worked for made a large amount of money out of the financial crash, while almost everyone else was losing it. The advice he gave to the Singapore government has made its response to the Covid-19 pandemic exemplarySetting a good example.; every other country should be listening to what he has to say.

Others argue that Taleb's arguments are of limited use. We all know that unexpected things are going to happen, but the more unexpected they are, the less we can do about them. He suggests that economists do more harm than good, but their theories are often more sophisticated than he gives them credit for. As for Singapore, it is always easier to control things in a small country.