Suspicion" traces back to the Latin word suspicere, which means "to look up at" or "to look at from below" and gave rise to the noun suspicio, meaning mistrust, fear, or a hunch.  This Latin noun transitioned into Old French as suspicion or sospeçon (the root of the Modern French soupçon).  It was borrowed into English around the 13th century (first recorded in manuscripts around 1290 as suspecioun), and eventually standardized into its modern spelling by learned scribes who wanted to reflect its original Latin roots.  

According to the Oxford English Dictionary (OED), the noun "suspicion" was first used in English during the late 13th century.  The earliest known recorded instance in the OED dates to around 1290 in a Middle English manuscript about Saint Sebastian.  The word was borrowed from the Anglo-Norman and Old French word suspecioun, which ultimately derives from the Latin suspectio.  The OED also has an entry for the verb form of "suspicion" (meaning "to suspect"), but it traces that usage much later, to a translation by Nicholas Ferrar before 1637.  According to the (OED), the adjective suspicious was first used in the Middle English period (1150-1500).  Its earliest documented appearance dates back to 1340, where it was used in the religious and moral treatise Ayenbite of Inwyt (meaning "Remorse of Conscience"). 

Suspicion in storytelling is a powerful narrative engine. It forces readers to actively engage rather than passively consume. By introducing doubt, you shatter the "single story" and force audiences to question motives, read between the lines, and hunt for truth.  

The importance of suspicion in writing stories:   
Engaging Cognitive Process: When a narrative presents contradictions or incomplete information, the reader's brain must work to reconcile the gaps. This active participation shifts the reader from an observer to a detective, deepening their emotional and intellectual investment in the story. 
Creating Psychological Suspense:  Suspense thrives in the gap between what a character knows and what the reader suspects. This dynamic relies heavily on two contrasting viewpoints: The Obvious Character: A character walks into a trap while the reader's suspicion—or outright knowledge—of the looming threat builds tension.  The Unreliable Narrator: Forcing the audience to doubt the narrator's sanity or honesty creates a lingering sense of paranoia. This makes every sentence a clue that must be weighed against the probability of deceit. 
Builds Rich Character Depth:  Characters who give off "untrustworthy vibes" instantly become more complex. Suspicion drives characters to test each other's boundaries, forcing them to reveal their true core values, fears, and hidden pasts when their motives are questioned.  
Enables Subtext and Thematic Depth:  Suspicion allows a story to operate on multiple levels. It acts as a bridge between the literal plot and the underlying themes. Readers who read "against the grain" use suspicion to uncover deeper truths about the author's world, whether that involves uncovering sociopolitical critiques, hidden biases, or the inherent flaws of human memory. 

Ultimately, utilizing suspicion—whether through plot twists, flawed narrators, or mysterious environments—transforms a straightforward tale into an immersive, interactive puzzle that stays with the audience long after the story ends.