Editor Nick Harrison has a post on how a writer should attempt to find the right editor or agent for his material, not just the first available. One editor may reject a manuscript or cover letter on a technicality; another may give it a chance.
The first commenter on this post, Tim Riter, offers this illustration from his experience. “For two of my books, I sent in a proposal to an editor, who promptly rejected it with the nicest form rejection letter. Within a year, at writers conferences I met another editor from each of those houses with whom she, I, and the book clicked, and the houses bought it.”