From skate to pork belly to razor clams, there's always something that's priced reasonably, previously ignored, and able to fill a role on a menu. That's where these things start. Your purveyor comes to you with a new product, say, Mangalitsa pork, and asks you to try it. It was almost extinct in Hungary as a lard animal but now they want you to experiment with it. There's an introductory rate. The pig really isn't good for much but lard, yet you can charge a premium for the experience and novelty. Call it "Kobe pork!" While the purveyor is showing it to you, he's showing it to five other chefs in your neighborhood: Boom. We have a trend.
A Chef Explains How Trendy Ingredients Hurt The Consumer