What are the most fundamental concepts in economics? Explain

There are a few definitions of economics, but they all revolve around the key concept of scarcity. Scarcity means that the resources of Planet Earth are limited, so it will never be possible for all of us to have everything we want. That scarcity of resources forces us to make choices.

The majority of economists believe that people are rational and will make those choices after a thoughtful cost-benefit analysis. So the second fundamental concept is one of the "rational economic actor," who always decides based on the logic of costs and benefits. Other economists are behavioral economists who specialize in the study of our non-rational choices.

One other key concept is that of specialization and exchange - the idea that the stock of goods and services grows when each of us specializes in what we do best and trades for the other goods and services we need.