A simple explanation is to attract more customers and expand sales. But if this is the goal, why not just reduce the price? This shows that this explanation is wrong. Another explanation is that McDonald's wants to discriminate the price by separating customers. Please note that it always takes some time to get coupons from McDonald's, rather than getting them at hand-browsing McDonald's website to find coupons, printing coupons, reading McDonald's promotional newspapers, or asking for them on the roadside all take a little cost, mainly time. Who is usually willing to spend these costs? Is a person with relatively cheap time cost. Who can go to McDonald's has cheaper time? Obviously, some low-income people-working class. In addition, coupons can usually be purchased from a specified combination of goods, rather than at will. In other words, customers who use coupons have to pay a price-the price of not choosing goods at will. This is also a cost. In short, there is a price to pay for using coupons-a price is also a price. In this way, McDonald's successfully distinguishes the rich and the poor among McDonald's customers. Then, for the rich-those who don't hold coupons, McDonald's offers them more expensive goods (no discount), while for the poor-those who hold coupons, McDonald's gives them discounts. The price of goods in the same place at the same time is different, which is a typical price discrimination. Through price discrimination, McDonald's squeezed more consumer surplus from consumers and increased profits. How to verify the above theoretical explanation? First of all, we need to introduce verifiable meaning from the above theoretical explanation: according to the above theoretical explanation, the poor should consume less, while the rich should consume more, so the total consumption of those who take coupons must be lower, while those who don't take coupons must buy more and more expensive things. This is obviously an observable significance. Secondly, whether the observed facts are consistent with the inferred observable meaning. This step is not difficult: as long as you find a good location and carefully observe the sales situation of McDonald's, you can know whether the verification results are consistent with the theoretical speculation.