I suppose that most people don't believe in sheer dumb luck. As for myself, I become more and more convinced of it. Let me share a few examples of why I have come to the conclusion there is such a thing.
Writer sends in what we refer to as a timeless piece. It can be used months from now. He wants it to go in a specific issue. That particular issue is already crammed full of editorial material. So it gets cut. Then the advertising department comes up short and wala the article is back in the issue. Sheer dumb luck.
College semester-long project is due next week. One student has been working all semester on getting audio (in the days before youtube or the Internet) and heavy research on jump rope "songs" and their origin. One student grabs a book on Navaho blanket designs. Writes up 2-3 page report on the dyes and meanings, draws and colors several different designs. Blankets gets an A, jump rope gets a C. Why? Professor is into Native Americans. Sheer dumb luck.
First novel. Action/adventure. First time author. President of the US reads it, likes it, mentions it...goes golden. Sheer dumb luck.
What else can you call it when your work wins some times and loses other times? As writers we tend to be mother hens over our work and get worked up when it's rejected. But maybe it's not your work that's lacking, maybe it's just sheer dumb luck.