This is a phenomenon that is difficult to justify. In all empirical natural sciences, whether physics, biology or chemistry, students have to do laboratory work since middle school. Economics is also an empirical science, but even if you enter the university, there is no experimental class. The real world is the laboratory of economics, in which everyone lives. However, university professors do not require students to observe everywhere and try to explain constantly. Those so-called "experimental" courses just take some figures I don't know how to get and do some statistical analysis. A true story supports my complaint. G.J. stigler, the master of price theory in the 20th century, is an expert who holds high the position of explaining price discrimination with different elasticity of demand after Mrs. J. Robinson. Once, when teaching the price difference in the Graduate School of the University of Chicago, Stella said, "We can't find two different prices of the same commodity in the same store at the same time. A classmate sitting at the back of the classroom raised his hand and said, "It's in the cinema near the campus, which means that ordinary people get 2.25 yuan and students get 1.25 yuan. Like movies, seats are first come, first served. Unable to respond, Stella walked up and down the platform for a few minutes, and suddenly said loudly to the classmate, "Tell you what, I'm going to burn down the cinema tonight!" " As all the students know, in any shop where customers can bargain, the price difference is an inevitable influence. How could Stella, who won the Nobel Prize in Economics, not know? In fact, from 1983 to 1985, I took my students to sell oranges on the streets of Hong Kong for three consecutive years, trying to spread the price. So I know that although different elastic coefficients logically support price deviation, in fact, different customers have different information costs and different bargaining time costs, and the differences of these restrictions are much more important to price deviation than the differences of elastic coefficients. A still famous article was written in the late 1970s. In the manuscript, the three authors cited examples of oil transportation to support their theory. They said: "oil companies own their own oil pipelines and don't rent them, but tankers rent them and don't own them." I am a consultant of several oil companies and wrote to the author: "All oil companies have their own oil fleets; Renting oil pipelines is very popular in the industry. "the article