The word strengthen comes from Middle English, formed by combining strength with the verbal suffix -en (meaning "to make").  The root noun strength traces back to Old English strengþu, rooted in Proto-Germanic and ultimately the prehistoric Indo-European root *strenk- ("tight, narrow").  

According to the Oxford English Dictionary (OED), the earliest known use of strengthened as an adjective is from 1578, found in the writings of the surgeon John Banister.  The verb strengthen was first used in English during the Middle English period (1150-1500), with the earliest recorded evidence dating back to 1450.  The word strengthening as a noun dates back to 1535 in Miles Coverdale’s translation of the Bible and as an adjective in 1571 in the writings of theologian William Fulke.  The noun strength was first used in English during the Old English period, or before 1150.  

The concept of being "strengthened" in storytelling refers to how characters, themes, or narrative structures grow more resilient, powerful, or profound through conflict.  This progression drives character arcs, validates core themes, and transforms passive plots into deep emotional experiences that resonate with audiences.  

Character Growth and Resilience:  
Overcoming trials: Characters face tests that break old habits and build inner power.  
Earning change: True strength comes from struggle, making victories feel real and satisfying.  
Proving themes: The protagonist's internal strengthening proves the main message of the story.

Narrative and Structural Integrity:  
Raising stakes: Each hurdle makes the ultimate goal harder and the narrative tighter.  
Deepening conflict: Stronger opposition forces characters to adapt or fail completely.  
Enhancing payoff: The final resolution packs a bigger emotional punch when the build-up is robust.