My housemate is sick. He's had a sore throat and flu for days, but man of might that I am, I feel fine.
"I wonder why I'm not getting it," I wonder aloud.
"I would think that's a good thing," he says.
"Maybe I shouldn't say anything," says I.
Without thinking, I'd fallen into the old taboo of not talking about things that you don't want to happen. Because talking about it might make it happen, you know. There are lots of superstitions against naming bad things. We say, "I won't talk about the deal because I don't want to 'jinx' it." Many cultures have superstitions that prohibit talking about the devil, calling him 'that one' or something similar. New agers try to think positively in the belief that the 'energy' you send out comes back. (Creating your own reality's a real bitch when you're just learning, isn't it?)
I think what's behind this is salience. When people cast about for explanations to what's happening in the world, they will naturally light on phenomena that are perceptually salient. That's what's behind the lunar fallacy. People incorrectly think that insanity, violence, and childbirth are more common during the full moon -- never when the moon is three-quarters and a half full -- because the full moon is more perceptually salient.
So is talking about something. And so the act of talking about an undesired event is wrongly blamed for making the thing happen. If I did get sick today, it'd be tempting to think: Hmm, I talked about it; that must have caused it. But I'd be ignoring the thousands of things I talk about all day that don't happen.