According to Wikipedia, a literary trope is a common pattern in literature. In fantasy novels, oft-used tropes include good triumphing over evil (often represented by a Dark Lord). Quests are a common trope as well. Also the poor unknown who turns out to be Royalty and saves the day when they figure it out. Magical items and prophecies tend to be important in a lot of fantasies as well.
I've been thinking of another one, but I don't know if it has a name. I can think of a number of examples of it, though.
Here are some of the elements: a person--often a child--always misunderstood, sometimes orphaned. This person has a special ability that they don't know about until Something Happens and they are whisked off to a wonderful place where they learn about this special ability and end up being part of something very important in saving their world as they know it. In fact, the world couldn't be saved without them.
Examples? Well, Harry Potter comes to mind as the most recent/ well known. But the trope is much older than that. Anne McCaffrey used it several times that I can recall: Lessa and Menolly in the Pern novels, Peter Redinger and the Rowan in the Pegasus series.
Mercedes Lackey uses it at least three times in the Valdemar series: Talia in the Arrows of the Queen trilogy, Darian in the Owl trilogy, and Mags in the new Foundation novel.
Holly Lisle's very first novel plays off this trope with the character Faia in Fire in the Mist.
I'm sure there are dozens more--probably more of them that I've read and just can't remember the pattern at the moment, plus doubtless many I haven't read.
This trope might be most common in fantasy, but I'm not sure. I don't read a lot else. I do know that The Secret Garden by Frances Hodgson Burnett fits it to a lesser degree. The world that little Mary saves is much smaller than all of Pern or Valdemar, but it is very significant to her.
What's so universal about this trope? I'm guessing that many of us have felt misunderstood and alone. If we were honest, I'm sure we've daydreamed about Something Happening and we could make a huge difference in our world. Wouldn't everybody wish they'd treated us better then?
What's your favorite trope? Or do you have any other examples of the one above? What about it appeals to you?