There is one principal issue of economics that exists at all times and in all places. This is the issue of scarcity. Economics (as a study) exists because scarcity always exists.
Scarcity is defined as the condition in which human beings' wants will always be greater than the supply of time and resources that is available to them. In other words, we always want more than we can possibly get. This is the basic problem of economics.
This problem is basic to economics because it forces people to make choices. We must choose, for example, whether to spend our money on a fun thing now or to invest it in our future -- we can't do both. We must choose to spend our time studying or playing -- we can't do both. Economics is the study of how people make these choices. Therefore, scarcity is the principal issue in economics that can never go away.