The financial crisis has reminded us of the valuable lesson that risks gone bad in one part of the economy can set off chain reactions in areas that may seem completely unrelated. In fact, risk managers and other executives fail to anticipate the effects, both negative and positive, of events that occur routinely throughout the business cycle. Their impact can be substantial—often, much more substantial than it seems initially.

At first glance, for instance, a thunderstorm in a distant place wouldn’t seem like cause for alarm. Yet in 2000, when a lightning strike from such a storm set off a fire at a microchip plant in New Mexico, it damaged millions of chips slated for use in mobile phones from a number of manufacturers. Some of them quickly shifted their sourcing to different US and Japanese suppliers, but others couldn’t and lost hundreds of millions of dollars in sales. More recently, though few companies felt threatened by severe acute respiratory syndrome (SARS), its combined effects are reported to have decreased the GDPs of East Asian nations by 2 percent in the second quarter of 2003. And in early 2009, the expansion of a European public-transport system temporarily ground to a halt when crucial component providers faced unexpected difficulties as a result of credit exposure to ailing North American automotive OEMs.