Plausibility is crucial for most fiction (the exception being comedy). If a reader notices implausibilities, their immersion will likely give way to questioning what they’ve just read. Too many of these questions, and the reader may well end up doubting the author’s ability to craft a compelling story.
The writer must make the audience’s leap of faith possible. (The Anatomy of Genres, John Truby)
Implausibility can creep into any area of a story: from how a character responds to a significant crisis to how they function anatomically. A writer may describe a character ‘laughing as they sneezed’ to inject humour into a scene; but how is a reader to picture this happening, given that sneezing and laughing are not simultaneously possible? Likewise, if a character falls down a rocky slope, it will be jarring to see no mention of their aches and pains. Writing impervious characters is a characterisation misstep:
A perfect character doesn’t seem real or believable. (The Anatomy of Story, John Truby)
Context, of course, is relevant. Yet even in high-concept stories, such as superhero narratives, implausibilities are passable only when they are justified by the story’s internal logic. If a superhero possesses extraordinary powers, the narrative must define these and remain within their limits. The same applies to technology:
This apparently simple fantasy adventure story has a strong theme that is concentrated in the symbol of the light saber. In this technologically advanced world where people travel at light speed, both heroes and opponents fight with a saber. Obviously, this is not realistic. But it is realistic enough in this world… (The Anatomy of Story, John Truby)
A diligent author will strive to eliminate implausibility from their fiction, though it is easier said than done, as even the most lauded of authors can err with implausibility: “Eagles, Explained”