The expression denotes a foundational, universally accepted truth or a statement of the obvious. It’s analogous to pointing out a readily apparent and undeniable fact. An example would be stating that water is wet; it conveys information that is inherently known and requires no further explanation or proof.
Its importance lies in its use as a rhetorical device to emphasize simplicity or to introduce a topic by establishing a common ground of understanding. Historically, such expressions have served as a starting point for discussions, ensuring all participants acknowledge a shared reality before delving into more complex or nuanced arguments. Utilizing easily understood concepts helps avoid ambiguity and sets a clear context.