Writing a story, is, at it's heart, an accepted way to lie to people. You make shit up, and tell it to them as if it really happened, and they accept that. Everybody knows this, but nobody really talks about it. Even those so-called 'true stories' are fabricated to a certain extent.
Some people don't like to admit it, and lash out when it's thrown in their face. Like Oprah did to James Frey. Twice. Fuck, I hate that woman.
Regardless, writers lie to people, and people pay them to do it. But there has to be some layer of truth to your story. You have to follow the basic rules of the world, or find a way to explain them so that the reader will accept the changes. Alligators can't speak English, and toes are not intelligent, individual beings. These are fundamentals, and you'd better have a good reason for breaking them.
Which brings me to the point of this post. The Ridiculous Premise. Have you ever read a really good book, and recommended it to a friend, only to have them ask you, "What's it about?"
You stall, and you think about it, and finally, sheepishly, tell them that it's about a guy who takes a lot of drugs, goes to Vegas to write a magazine story about a desert race, and proceeds to get completely lost in a fugue state of self-medication, paranoia, and petty lawlessness.
Sounds rather juvenile, yes? That's Fear and Loathing in Las Vegas. Great, great book. But you have to be honest, the premise is kind of.... well, ridiculous.
The great thing about this whole concept is, it doesn't matter what your story is about, what matters is how it is written. Also, very important, is that you have some explanation as to why the ridiculous is happening. It doesn't have to be a solid explanation, but as long as the reader can accept it, you're golden.
There are millions of stories and legends from around the world that can help you with this. Everyone knows that vampires can't come into your house uninvited, but how many know that they can't pass any doorway if it is lined with salt? How many people know that a broom falling in the house means that company is coming, and not likely welcome company?
Everyone knows about Fairy Rings, mushroom patches in circular shapes, but not many know that in some Austrian areas, it is believed that dragons make them, and once one is made, nothing but toadstools will grow there for seven years, or that the Dutch believe they are where the devil puts his milk churn? I'm guessing, outside of Austria or the Netherlands, not many do.
Enough people will catch it, though, to validate your story, and the mythology that you are creating. Others will look into it, and confirm your statements independently. Still others will believe you out of hand, and spread the tale themselves. The point is, you've taken something old and not widely known, and used it to hold your ideas together, and tie them to the world that your readers understand.
Any time a story is read, there is an unspoken agreement made between the reader and the author. The author agrees to tell a story that the reader will be able to follow and understand, and the reader agrees to suspend his disbelief enough to accept the tale as it is told. If one side or the other breaks that agreement, or pushes it too far, it will end up as an unpleasant experience. How many books have you set aside, unfinished, because you simply did not enjoy them? How many of those did you not enjoy simply because you couldn't believe the premise, or the actions of the characters? Either the writer pushed you too hard, you couldn't extend your disbelief far enough, or, in some cases, there was just a unconquerable disparity between what you believe the boundaries are, and what the author believes them to be. It's unfortunate, but it happens.