'People burn out. You can't do that job for a long time'

"I was not cut out for Wall Street," Nassim Nicholas Taleb says. Wall Street agreed. At first, he could not get a job as a trader. After he finally cracked New York's financial heart, he found he also had problems when trading in Chicago; another trader tried to strangle him and it took four security guards to drag his assailant away.

As he explains in Black Swan (just out on Penguin, £8.99), his fierce-fingered rival was furious about his standing in the wrong place in "the pits". A "black swan" is a totally unforeseen event such as September 11 – or, indeed, a fellow trader grabbing you by the throat.

Despite all that, Taleb was clearly much better in the financial markets than he makes out. He went on to become the author of the bestselling Fooled by Randomness and also a University of Massachusetts Amherst professor in the wonderfully named discipline Sciences of Uncertainty. And, on one recent Monday morning, he was a guest on BBC Radio 4's Start the Week programme.

Taleb left Lebanon as a teenager and had taken an MBA at the prestigious Wharton School in Philadelphia before knocking at the door of Wall Street.

"I went to work for a year as a trainee banker in New York – the worst job." One day, he bumped into a man who worked for a French bank and they chatted (as you do) about risk assessment for a financial portfolio. Taleb was hired on the spot and now he was in the money markets. For 10 years, he operated as a "quant" and a trader.

He explains "quantative finance" as applying mathematical models of uncertainty to financial data. Unusually for a "quant" he also traded, but he was the opposite of Nick Leeson and that wild French speculator who recently created a financial black hole. Taleb specialised in hedging his bets: if he sold an option on one currency going up, he would make sure he was covered if it didn't.

Did things go wrong? "All the time. For 10 years I worked full-time; I would arrive at seven o'clock and leave at 5.30 or six. I would gain eight pounds a year on average, owing to the sedentary life and eating too much.

"People burn out. You can't do this for a long time; it's like being a taxi driver in New York, or a mercenary, or a highway robber. I worked at it for a little longer than I had intended to, but you can't predict circumstances. I meant to write, and I never lost sight of that dream."

Taleb scaled down his financial work but he remains an investor and a consultant. His Wall Street experiences made up the bricks of the new career he built as a theoretician.

Many people, he says, stay trapped in their money-making professions and fail to get out in time to do the creative work they'd planned. Look for the next new thing. No, he doesn't know what it is. It'll be something unexpected, of course.