Murphy's Law is usually quoted as "Whatever can go wrong, will go wrong" but that, as many of you probably already know, isn't correct. The real Murphy's Law is "If there's a wrong way to do something, someone will do it that way."
One version is fatalistic, the other, deterministic. In the fatalistic version, it’s out of your hands. Prepare if you want, but the fates decide. Not your fault. The deterministic version is both reassuring and a little scarey. Reassuring in that, one does have a say in the matter and can make a difference. Scarey in that, the difference one can make is often to make things worse. Any decision you make has the potential to be the wrong one but, unless you're a politician or a ceo, there's no one to blame but yourself.
So what’s this got to do with writing? Everything. As others have pointed out, a writing career is primarily a deterministic occupation and ultimately you’re responsible for its success or failure. Talent is important, but not enough. Hard work is absolutely necessary, but also not enough, or at least not always. Things go south. It’s comforting to blame the economy, and the editors who are style/story deaf in your range, and the publishers who treat your books the way a wholesaler treats one more sack of flour, and the reviewers who only like, say, paranormal romance and had no business reading your alternate history novel in the first place. All that happens. Constantly. They are both unfortunate and annoying, but not one of those things can derail a writing career the way you can.
I’m not talking about avoiding mistakes. You can’t do that, no one can-you’re going to screw up, so deal with it. You’re going to forget a deadline, or come up blank on a theme so a prestigious anthology goes to press without you. You’re going to make a social oops at the Mill & Swill and convince an important editor that you’re a twit. Those things happen and there’s no avoiding them. It’s part of the human condition. Just take a deep breath and try to contain the damage, but otherwise don’t panic. These sort of things, while serious, are not career killers.
So what really kills a career dead in its tracks? You do. And you do it with a simple failure of nerve. How do such things manifest? Mainly not by what you do, but what you don’t do. It’s the book you didn’t send to the publisher you really wanted because you were afraid they’d say no. It’s the story you didn’t write because you didn’t think there was a market for it. It’s the chance you didn’t take because you were too afraid of feeling foolish. It’s too many times you played it safe rather than reaching for a theme/story outside your comfort zone because you had a sure sale by sticking with what you’d done before. See the pattern? It’s you, never giving yourself enough credit, never quite believing that your reach always has to exceed your grasp, never quite believing in yourself when you’re the only one who can.
If any of this sounds too close for comfort, fix it. I’m serious. I don’t claim to know very much, but I do know this. These are the sorts of mistakes you have to first recognize as being mistakes, and understand that you don’t have to keep making them. These are the kind of mistakes you can learn from, and more to the point, you have to learn from.
Or, as they say, ELSE.