Writing tools of "show" or "tell" serve important and very different purposes. They complement each other, and when used with skill, they advance a plot effectively.
Showing creates emotion in readers—that flush of heat in a woman reader’s face while experiencing a torrid seduction scene, or anger shared with a main character who suffers the sting of torture at the hands of a hated antagonist. “Showing” supplies details of the character’s experiences in such a way as to allow the reader to supply emotional reaction.
Telling does not trust readers to reach the author’s desired emotion. Instead, it “tells” readers how to feel. On the surface, this sounds less effective, but there are two distinct benefits of doing so. First, telling is efficient. It wastes no words and pushes plot forward with as little loss of reading time as possible. Second, telling moderates the relentless emotional assault of showing by creating a welcome break for readers in an otherwise fast-paced, emotion-laden story.
Pretty simple, huh? Showing generates emotion in readers. Telling moves the story faster and reduces emotional impact. When combined properly, storytelling wins.
Let’s have a little literary fun with an example.
Tell: Mary saw Matthew's body as she entered the room. She dropped to her knees and gagged, nauseated by the smell. Vowing retaliation for the killing of her only brother, she promised to deliver revenge against her brother’s killer, Demonis Maximus.
Show: "Oh, my God", Mary said upon entering the room. She dropped to her knees, ignoring the growing pool of Matthew’s still warm blood. Brushing back flies that swarmed on his wound, the stench of death gagged her. The dead man’s youngest sister shook her fist in the air. “My brother’s murder came by your hand, Demonis Maximus,” her words forced through clenched teeth. “I swear on the grave of our mother, you shall die by my doing.”
Which is best? Showing her angst . . . or telling the reader of her pain and promise of revenge.
Answer - NEITHER.
If this drama is not essential to advancing the plot, then it must be informational in nature serving only to link more important plot elements. In that case, telling advances the story faster and does not generate wasted words for the reader or unnecessary emotional angst.
On the other hand, what if the plot relies on Mary’s hatred for Demonis Maximus to provide motive? Or, perhaps the writer’s goal is as simple as character develop in building compassion for Mary. In either case, her reaction to Matthew’s death should be “felt” by the reader. "Showing" the MC’s suffering allows the reader to share the same breadth of emotions as Mary did.
One word of caution—"telling" can insult a reader's intelligence. If the author does not trust readers to experience the desired impact, and simply tells them what to think, then some readers will drift out of emotional connection with the main character(s) or the storyline. By the same token, excessive "showing" can get annoying. Meaningless dialog, or repetitive, yet unnecessary drama, actually diminishes impact as it wastes the reader's time.
These distinctions of show or tell apply to omniscient narration as well. A narrator can say (telling) it was a beautiful day, or this unseen story-teller can describe elements of a beautiful day (showing) and trust the reader to reach the desired conclusion.
Show or tell? That is the secret of the best-selling authors I have read. Every great writer seems to find just the right balance between showing and telling. They know when to ramp up the emotional impact with dramatic showing and when to “tell” the plot forward to give the reader a breather before the next high-energy scene.