I’m convinced the superstition is a misunderstanding over time of things that were, on their own, bad luck. Salt used to be expensive, so spilling some was bad luck because you would have rather kept it all for use instead of wasting it.
Mirrors would have also been expensive, especially when they needed to be transported before the time of smooth suspensions. The whole 7 years thing could be from it taking around 7 years for one particular broken mirror to be replaced.
Or the ones that invite accidents, like walking under a ladder (which usually implies someone is working at the top and might drop something, so odds of death are a bit higher under ladders). Or opening an umbrella indoors, where things are more crowded and you might injure someone or break something.
Though the black cat one is probably just racism.
Anyways, I bet that’s where they started and then humans being kinda (or very, depending on the circumstances) stupid and liking jumping on bandwagons they don’t always understand to fit in, left us with some people thinking those things cause ghosts to haunt you or whatever dumb shit superstitious people think happens.
Though I do think it is a bit wasteful to just dump salt out on the ground.
“Luckily there was a loophole in those rules that I (omnipotent, omnipresent, and omniscient) made.”
If that doesn’t scream, “made up by the clerics trying to avoid contradicting each other and bringing the whole house of lying cards down as they went”, just keep sending money to your church. Because if a god needs anything, it’s obviously worldly riches and unquestioning loyalty. We need these churches to impress everyone with the power of our god, but he’s sleepy after making it all and throwing tantrums bigger than we can imagine because people were acting like the way he made them capable of acting, like cartoon villains in some cases, like a whole city whose first reaction to seeing an angel was “Let’s all rape it!” So that’s why you need to send your money without any questions!