The productive value of physical labor as such is low. If the worker of today produces more than the worker of fifty years ago, it is not because the former exerts more physical effort; quite the contrary: the physical effort required of him is far less. The productive value of his effort has been multiplied many times by the tools and machines with which he works; they are crucial in determining the economic worth of his services. To illustrate this principle: consider what would be a man’s economic reward, on a desert island, for pushing his finger the distance of half an inch; then consider the wages paid, for pushing a button, to an elevator operator in New York City. It is not muscles that make the difference.

- Nathaniel Branden. Capitalism: The Unknown Ideal (1966).