I’ve broken several mirrors in my life but I’m not quite sure if the 7 years bad luck which is supposed to result from it runs concurrently or consecutively. Of course it’s no surprise it’s hard to get clear empirical answers from believers in this superstition because superstitious beliefs come from not looking for ways to prove your theories wrong.
Most simply superstition is counting only the hits and not the misses. It’s the failure to account for the chance it would rain independent of your rain dance. However superstitious thinking isn’t really a certain set of beliefs but a claim about how one can come to know things. One can easily be just as superstitious about how to get your failing car to start, with no appeal to the supernatural, as you can about the effectiveness of prayer, which has an explicit appeal to supernatural entities. Once you fall into superstitious thinking, by not counting anything against your theory, you are guaranteed to see everything as confirmation of your theory but this is a mere psychological trap influenced by cognitive biases.
You have a friend Jason Voorhees who says he’s figured out what dark matter is and the precise role it plays in the current understanding of physics (and of course how to return from the dead). Stunned, you demand to know how he figured it out but he refuses to tell you or anyone else. Jason says his solution only makes sense if you accept his solution without attempting to verify it. This, you rightly think, is plainly ridiculous. You have no reason to believe he’s solved the problem if he is unwilling, or unable, to provide evidence of his claim. One could only imagine how brutally Jason would be received if he tried that type of reasoning at a scientific conference.
This is exactly the type of response you are likely to get from someone who is superstitious. It’s the type of answer we often get from believers in psychic powers, prayer, curses and athletes who think filthy undergarments help them win games. A world in which some force works in ways which can’t be statistically detected is indistinguishable from a world in which that force doesn’t work at all. Getting people to acknowledge this trap is the first step to getting them to drop their superstitious beliefs.