How plausible does a novel have to be? Obviously not very or Candide, A Hundred Years of Solitude, or The Time Traveler's Wife could not be read. So maybe the question should be: At what point does the reader throw the book across the room?
I have just read Orson Scott Card's 1977 science fiction novel Ender's Game. I suspect virtually everyone else in the world has read it, but let me tell you what's wrong with the
Most of the novel describes Ender's training in Battle School. One of the novel's conceits is that Ender must be kept ignorant of the training's real goals. He must be tested, and tested, and tested until he is as strong as the steel in a samurai sword. Indeed, toward the end of the book one of Ender's fellow trainees threatens to kill Ender. And this is not a game. Card presents the situation as a genuine possibility. Cooler heads argue with Colonel Graff that he is going too far. He argues that if Ender thinks someone is going to step in to save him at the last moment, all his training will be wasted. Ender must believe he must kill or be killed.
What happens if Ender is killed? Humanity's only hope dies with him. There is no other leader. It's Ender or none. What demented military officer would risk all of humanity on the possibility that a school bully will kill the one individual that could make a difference? (Throw book across the room.)
If that's what's wrong with Ender's Game, what's right with it? It remains popular. It's still in print almost 30 years after publication. Hollywood made a movie of it in 2013.
My theory: It appeals to 13-year-old boys (and adults with the emotional maturity of a 13-year-old). The adults and older boys around him don't understood the hero. They don't realize that he is special. And not just special, the savior of humanity. The ordinary readers of Ender's Game don't care about the holes in the story (if they even notice them); they ignore questions about the Second Warsaw Pact(!); they accept the casual violations of known physical laws. Ender is the hero of this fairy tale. He does disable his tormentor at the end of the book—in fact, unknowingly kills him—and he saves humanity by—again unknowingly—virtually exterminating the race of alien buggers.
I wish I had the talent (skill? luck?) to write something as popular.