"Let them do" belongs to Adam Smith, the founder of economics science according to some ...
Later on, big economies have been rescued from WWII crisis by Keynes who provided a different approach for the explanations of economic.
So, there are two main theories to explain macro economic processes. The former is defined as the classical theory and the latter as the modern one.
Adam Smith advocates for invisible hands and expresses self-interests will create community benefit in brief.
Keynes states there is a need of intervention to the economies.
