New writers like to believe that editors and agents are super-human beings who know everything. They certainly know better than writers. Heh. The truth is, selling your writing is often a matter of luck.
Editors and agents have problems even as you and I do. They have jobs to do, and they want to do them as easily and as quickly as they can, with the least amount of hassle. This means that when you send an article proposal to a magazine and another writer sends a similar idea, if the publication has worked with him before, he gets the job. It may not be fair, but to the magazine he's a known quantity. They know what to expect with him. On the other hand, if there's a book on the topic and the agent calls to offer the serial rights for less than it would cost to hire either of you, you both lose out.
Rejection is a fact of the creative life. Many genre novelist have written ten complete novels before the first one sold, and that sale was often a matter of luck. That novel was in the right place at the right time, so to speak. Let's see, at 80 to 100 thousand words per novel, that's close to a million words, before a single word sold. Of course, once a novel sells, the editor and the writer's agent will encourage the writer to dig out those past efforts, revamp them, and chances are they will be published too. (So if you're filling a couple of filing cabinets with unsold manuscripts, take heart. Look on them as your retirement fund. :-))
Many writers have to continue for years, doing what isn’t working. They have no guarantee that it will EVER work. But if they stop digging that hole, they'll never strike gold.
Discover how to sell your writing in "Help – My writing's not selling."