When an audience says a story isn’t believable, it’s never because the story is too far fetched. It’s because it’s not consistent with the characters and story you’ve designed.
We’re happy to put our trust in the hands of the storyteller and believe him when he tells us that Marty McFly travelled back to November 1955. We buy it completely when Obi-Wan introduces us to Han and Chewbacca. But a modern story in the same street we live where the character doesn’t go after the girl can be unbelievable.
We feel it. It’s an instant reaction of – “he wouldn’t say that. That’s not how he feels.” It’s similar to a painter trying to force a sketch into a painting and clashing with the rest of the oils on the canvas.
Sometime’s it’s idea the writer clings to from a previous draft. Sometime’s it’s just a scene or action that’s not developed. It’s always a forced action or an element of the story that isn’t true to what we already know.
The audience wants to believe. They want a good story. They will go along with your story no matter how far fetched just as long as its consistent with what you have already developed.