Something similar happens to people who take volcanic rocks from Hawaii. They suffer ill fortune and are convinced that Pele has cursed them, so they mail back the purloined rocks. If you are convinced that something is cursed, you will notice evidence that "proves" it is cursed. People are more likely to notice bad things that happen on the 13th of the month, especially if it falls on a Friday. A team that hasn't won a championship in a long time, or can't seem to win, must be cursed. And so on.
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