The line sets out a rule with a boundary attached. Explanations and designs should be stripped of anything unnecessary, because surplus detail obscures what is actually doing the work. The second clause supplies the constraint: reduction must stop at the point where the account no longer covers what it is meant to cover.

The distinction is between simplicity and oversimplification. A model that omits an inessential feature becomes clearer; one that omits an essential feature becomes wrong, while often appearing more elegant. Because both moves feel like refinement from the inside, the difficulty lies in identifying which components can be discarded.

The principle is widely applied beyond physics, in engineering, design, writing and teaching, where the same tension arises between making something accessible and keeping it accurate.