Suspension of Disbelief
The suspension of disbelief is what supports the contract between storyteller and listener, where the storyteller is allowed to take certain liberties concering the realism of the story so long as the story is consistent with pre-established agreements.
Without a believable story, suspension of disbelief will be broken and the listener will feel that the storyteller has lazily broken the rules of their own universe.
Believability relies on the storyteller presenting the 'rules' of the fictional universe before they have any significant effect on the plot. As long as this is done, the storyteller may stray from reality by large strides.
A listener enjoys surprise. But a surprise that does not adhere to the pre-established rules breaks the suspension of disbelief, and is therefore not as enjoyable due to its unpredictability.