Multiplication — that's what people don't understand about Ebola, according to Nassim Taleb, the author of "Fooled by Randomness" and "The Black Swan."

More specifically, Taleb explained to Business Insider that many people talking about the disease don't "have a grasp of the severity of the multiplicative process."

The argument that the US should be more worried about a disease like cancer — which has more stable rates of infection than Ebola does currently — is a logic that Taleb calls "the empiricism of the idiots."

The basic idea: The growth of Ebola infection is nonlinear, so the number of people catching it doubles every 20 days. Because of this, you have to act quickly at the source of infections, he says. "The closer you are to the source, the more effective you are at slowing it down ... it is much more rational to prevent it now than later."

The problem Taleb sees is that if there is not more urgent action in Liberia, Sierra Leone, and Guinea — to the point of restricting travel and other measures that may now seem like an overreaction — then there will be consequences here.

"If you have to overreact about something, this is the place to overreact," he said.

If Ebola doesn't get contained at the source now, he says, there is a risk that people start perceiving it as out of control, and that could have major economic consequences in the US — shutdown airports, people too afraid to go out of their house to buy anything, and so forth.