The article explains how we can figure out what people want and how prices affect their choices by looking at data from real markets. By studying how people's demands change when prices and incomes go up or down, we can understand what they prefer. The researchers found that by observing what people own and the prices in the market, we can figure out exactly what they want to buy without needing a lot of data. This helps us predict how people will react to changes in prices and make better decisions in the market.