Effective policymaking

In my graduation days my economics teacher used to tell me that there is just one main law of economics- Demand must equal Supply. A number of economists have started thinking about economics as a study that can help explain why demand and supply mismatch. It is often said that the main job of an economist is to explain why his earlier prediction failed. But economics is not as easy to understand as science. In a typical chemistry experiment you can be sure that the elements that you are mixing will create a new compound and the results will vary as you keep changing the experiment conditions such as temperature, pressure, etc. In an economics experiment you cannot predict the outcome easily as the elements (individuals) react differently in different conditions (conditions that can vary by region by economic growth and development). For example, an individual in USA may not be great saver but an individual in India may be. An important consideration while making any economic policy is to understand the behaviour of the individuals in that society. This is exactly why some policies are more effective in some places!