As long as Human Consideration of Existence, remains arbitrary, as in Physics ... being the Science of the Physical ... there is to be, so to speak, no end to its applied "Practice" ... Essentially a search for Physical's Logical Ideal.
Meaning, each "New" becomes a Physical "discovery" ... everything, discovered, then has to be taken individually, quantumized, theorized, and applied, in a vast, an incalculable Isolation.
Physics at its Logical best, attempts defining the Existential's Reality, within the False Premises based, Theories of Relativity, and Quantum Mechanics.
Thus, there is neither, nor ever will be ... "a Key thing'' meaning, a Theory of Everything ... Defining the Totality ... for the Reality, stands Defined, and Governed by The Law of Creation, Defining, Everything Created: and we know The Law Intrinsically.
The Law, of Everything, Hath been stipulated in the Koran ... I quote:
"Praise Thine Lord Hath Created In Pairs The Totality" ...