Wow Clare! You summed that up pretty well!

I just figured that if someone did something that was not his usual habit, and then something bad happened, he might think that the break in habit caused the event.
And if he did something twice, and something bad happened both times - well, it was pretty much set in stone!
And of course, gossips loved to wag their tongues and say that so-and-so did such-and-such and guess-what-happened?!
And the rest was "history."

As Clare said, yes, a desperate attempt to explain one's fate or to control one's future, or to just explain the unknown.

...And then there are those of us who love the number 13, walk under ladders every chance we get, and cross a black cat's path several times a day!

(Come to think of it, that could explain a lot...

)