The occasional spectacular random success is far more memorable than a string of failures, because the string of failures simply proves the ritual wasn't done correctly. Or there's some other unknown reason why it didn't work.
It's also known that rewarding a behaviour at random is better at reinforcing it than constant reward - perhaps because the reward stimulus is fresh each time it's re-experienced.
https://www.schneier.com/blog/archives/2006/11/perceived_ris...
The one-off event of rain forming becomes the story that everyone remembers most and is passed down with dogma. It gets lots of momentum. Day-by-day data generated for years and analytically processed isn't quite memorable. This is same reason people are more afraid of airplanes despite cars killing more. More relevant, it's the same kinds of bias that makes people think they'll win it big in the lottery despite all evidence to the contrary. I've walked in on 50yd lines when PowerBall is up. They'll always say "But such and such up North won $100mil. You never know. It can't hurt to try."
Illogical as hell given that time and money could produce real benefit with high certainty. Yet, they continue doing it to try to re-create that one-off moment someone else experienced. And then someone else experienced it again. :)
That's a great example given it is long-term, repetitive, and even non-experts should understand it. I'm going to try to remember it.