The TVTropes Trope Finder is where you can come to ask questions like "Do we have this one?" and "What's the trope about...?" Trying to rediscover a long lost show or other medium but need a little help? Head to Media Finder and try your luck there. Want to propose a new trope? You should be over at You Know, That Thing Where.
It sounds like you're talking about Deconstruction, and if the purpose of an entire work is to deconstruct a specific genre (such as fantasy), then it'd be Genre Deconstruction — or Deconstructive Parody if it's Played for Laughs.
Take for example the classic Don Quixote, which is a genre deconstruction of Chivalric Romance (among other things). Mr. Quixote's romanticized view of the world has little relevance to real life, and eventually his friends (the rational side) are able to reign him in peacefully before he gets himself (or someone else) killed.
Low Fantasy in general would also tend to take a somewhat less romanticized view of chosen ones and prophecies, although usually it's not out to deconstruct the whole genre. It wouldn't be out of place to have a prophecy pop up, and for most of the characters to treat it with the credibility of a telephone psychic. For example in the book Dragonsbane (a low fantasy novel), the world's only known dragonslayer is treated by the public as a storybook hero with divine blessing (romantic side), but when met for real, he is a skilled warrior, yes, but freely admits to being a humble Combat Pragmatist who used every dirty trick he could think of (rational side).
Edited by KD
Thanks, that seems to be right.
I would like to know if there is a trope or genre covering the dismissal of fantasy tropes. As an example say there are two sides to a narrative, the “chosen one” who is guided by prophecy to lead his people against another country, and on the other side a country whose philosophy does not follow a fantasy model. The story progresses but in the end the “Chosen one” and his people fail because their actions were guided by devotion to outdated directions. Prophecies are nonsense as realistically you can’t predict the future. I discovered rational fic but this doesn’t quite fit as it involves allowing the reader to follow step by step to reach a conclusion. I also don’t believe such a thing as an author polemic is quite right. The story isn’t out to mock belief, it’s just that the motivation of one side has no merit. The rational side bears no malice towards the other they’re just not prone to flights of fancy. I’d like to read such stories but am not aware of any examples. I realise such a genre would go against the needs of a traditional narrative structure, or risk alienating potential readers.