Economist want to base their explanation of how much people want to buy on the foundation of:
irrational behavior. costs and benefits. habit and fad. manipulation of people by marketers.
Mary is having the yard sale and is willing to sell a painting if she gets at least $2, but she has not marked a price on it. John is at her sale and willing to pay up to $100 for this painting. What can economic theory tell us about the price that will result?
It will be $51, half way between the values that Mary and John place on the painting. There will be no sale because these two values are too far apart. If there is a sale, the price will be somewhere between $2 and $100. Nothing; economic theory can only explain markets with many buyers and many sellers.