An intellectual is going to have doubts, for example, about a fundamentalist religious doctrine that admits no doubt, about an imposed political system that allows no doubt, about a perfect aesthetic that has no room for doubt.
We think of prices as simply the notation of how much we must pay for things. But the price system accomplishes far more than that. Hundreds of millions of people buying and selling, and abstaining from buying and selling, generate a system of signals - prices to producers and consumers about relative scarcities and demand. Through this system, consumers can convey to producers their subjective priorities and entrepreneurs can invest accordingly.