America's leading management theorist, Scott Adams, has claimed that you have to be popular first before you can start being any good. His examples are mostly TV shows. His argument is that even a really good show will probably be cancelled, unless people can sum up what it's about in a sentence that makes other people curious to watch it.
The analagous problem for works of literature is the problem of pitching. Novice authors imagine publishers will read their books, then publish them if they're good. But the supply of books by novice writers is so large that agents and publishers don't have time to read most of them. So typically, unless you're already somewhat established, agents will decide whether to take a look at your manuscript based on whether its one-or-two-sentence description sounds catchy.
Adams writes, "I have a twofold test for whether something can obtain instant popularity and thus have time to achieve quality: 1. You must be able to describe it in a few words. 2. When people hear about it, they ask questions." From the comments on Adams' blog, it's clear screenwriters don't think this is news.
At a conference recently, a writer friend told me, "I could make up an idea for a book in a minute that I could pitch to agents, and I know it would be a more interesting pitch from their point of view than the pitch I'm actually able to make, for this memoir I really care about that I've been slaving on for years!"
It's always instructive to compare the view from both sides of the gate, so kudos to San Francisco agent Nathan Bransford who will be holding a "Be an Agent for a Day" contest on Monday. On Monday he'll post fifty queries and you have to put yourself in Nathan's shoes and pick the five that'll keep him in business -- there may be a prize for picking the right five.