The word calmness combines the root calm (from the Late Latin cauma, meaning "heat of te midday sun") with the Old English suffix -ness which denotes a state or quality.  Historically, intense midday heat in the Mediterranean caused winds to stop and the sea to grow still, shifting the word's meaning from "burning heat" to a "quiet, resting state".  The shift from describing weather or the sea to describing a peaceful human mind occurred around the 1560s.  

According to the Oxford English Dictionary (OED), the earliest known use of the derived noun calmness is from 1516 in the writings of the printer and publisher Richard Pynson.  The base noun calm first appears in 1393.  The verb calm appears in 1399.   The adjective calm appears in 1440.  The earliest recorded use of the adjective calming is from 1651.  The related noun form of calming first appears later in 1699.

The concept of calmness in storytelling acts as a structural anchor that gives meaning to action. Just as music requires silence between notes to create a melody, a narrative requires moments of stillness to give impact to its conflicts.  

Emotional Counterbalance:  
Accentuates chaos: Constant action leads to audience fatigue. A period of stillness makes the next dramatic peak feel far more impactful.  
Allows digestion: Quiet scenes give the audience time to process major plot twists or emotional shocks.  
Builds tension: A lingering, quiet moment right before a conflict creates suspense, often making the silence feel louder than an explosion.  

Character Depth and Realism:  
Facilitates reflection: True character growth often happens during internal, calm moments rather than during chaotic action sequences.  
Reveals vulnerability: Stripping away external conflict forces characters to confront their raw thoughts, fears, and grief.  
Establishes normalcy: Showing a character in a peaceful state sets a baseline, making it clear exactly what they stand to lose when the conflict begins.  

Pacing and World Building:  
Enhances immersion: Calm scenes allow the author to describe sensory details—like the sound of rain or the smell of coffee—which grounds the audience in the world.  
Dictates narrative rhythm: Mastering the shift between high energy and deep calm creates a compelling "heartbeat" for the story.