Answer:
they work in their own self-interest
Explanation:
The total that an economy produces consists of the sum of all the goods and services produced over a period of time. Thus, all the work of each individual contributes to the economic development of a country. This was explained in the early days of the study of economics as a science, theorized by Adam Smith, which said that every human being is selfish and works to seek what is best for himself, but that individual selfishness of all together would contribute to development of a nation's economy. This is in the book The Cause of the Wealth of Nations.