Disambiguate: Action is a physical quantity that encapsulates the dynamics of a system. This quantity is the central one in the quantum revolution, and we will have many things to say about it. But first we want to talk about action in the even more general sense.
Wikipedia article on Frederik Sibbern: “Viden er til syvende og sidst kun til for at skabe mere fuldkommen handlen, mener [Sibbern], og med denne tanke for øje har han formet alle sine værker.”
“What I really lack is to be clear in my mind what I am to do, not what I am to know, except in so far as a certain knowledge must precede every action.” (Kierkegaard)