What is the rationale behind differentiating long-run and short-run in macroeconomics?

In macroeconomics, short run and long run are essential to differentiate. There are many things that occur in an economy but cannot be examined or analyzed in a short span of time or within a year. In the same way, people need time to adapt to changes and become familiar to them, accept them in their daily course of life and so on. In short, every happening cannot have an immediate impact on the economy, the results of which can also not be seen in the same time.

The short run looks into the changes and immediate responses occurring in the economy as well as the changing expectations and preferences of the people.

The long run, on the contrary, looks into the procedure of reaching at the equilibrium after looking into the detailed information, and the first and second order conditions of an occurring event.