I was thinking about this when I almost had to walk under a ladder the other day (and get bad luck). That one seems like an oral story that arose from people being hurt, whereas crossing the path of a black cat, while also supposedly bestowing bad luck, seems to have no plausible rationale.
I like this thought. Maybe some things are just like astrology, just Schelling points that everyone decided meant something, and simple "heightened awareness" gets scaffolded into it. That heightened awareness is the selective pressure for a set of observations to persist, even if arbitrary :) but sometimes there's a rhyme to the reason, and something that cant be clocked to one thing is somehow at the center of an idea