So I was wondering about how I could use this phenomenon in understanding and writing about people. Here are my first thoughts. I cite "magic" because I was prompted to ponder by the "magic" arts above.
A "magic", or mystical art is going to have people who make rules for it. Even absurd practices like reading tea leaves would have practitioners an proponents who feel more confident in readings that are "properly prepared". Now I don't know anything about reading tea leaves, so I'm just making up some example rules.
A tea reader could require that leaves are boiled over the flame of a balsa wood fire, or that the leaves must be boiled, chilled, and then reboiled to increase the accuracy of the reading. Or they might claim that the readings just won't work unless they use distilled water, or water that has been purified by the light of a full moon.
These requirements serve many practical purposes. First, a complicated process makes the practitioner sound like they know what they're doing(this is important whether the practice works or not). Second, more difficult processes give us something to blame if the spell works or make it difficult to duplicate (hence test). Third, we naturally try to explain why things work. We want to believe in some things even if they aren't real. As a teen, I was convinced that if we approached a certain intersection behind a truck the light would be red. But if we were not following a truck it would be green. I mentally tracked what happened each time we went to that intersection. Very often my superstition was correct. And when it wasn't, I overlooked the result or tried to explain it away.
Here's another anecdote from one of my German professors in college. He was in Germany as a religious representative and was eating dinner at the home of a local congregation member. This particular family believed that drinking water after eating fruit will kill you*. My professor didn't know about this superstition, and so when he asked for a drink of water after eating some fruit the family balked. He waved away their concerns, but they persisted. They even cited examples of distant relatives who had died to prove their point. To prove them wrong, he drank the water though they made it clear that he was doing so against their advice and they would not be held responsible for his death.
The next day my professor returned to the family home, thinking that his survival would be enough evidence to clear their muddled thinking. When they opened the door and saw him standing there, happily alive, they claimed that he was protected by God because he was a religious representative.
Now, I don't personally believe that drinking water after eating an apple will kill me. But I don't fault these people for believing something so completely ingrained. Perhaps they eventually cast off that belief, perhaps they didn't. I do believe that there are absolute truths, though I'm pretty sure that most of us only have a few glimpses or shadows of what they really are. But I don't blame people for believing the traditions of their ancestors.
What interests me here is how far spread the belief in things that we don't understand, and the effort to categorize random events is. We even find it in our modern "enlightened" world. People make a decision and then support their ideas with arguments. Sometimes we even look for research that will support our own position.
If you're creating a world, don't just think about the facts of the world. Consider how the people in your world try to understand the chaos around them. Which beliefs are real, and which beliefs are founded on a misinterpretation of tree bark? And more interestingly, where do those lines cross?
*FOOTNOTE: From all the Germans I've talked to, I don't think that this is or ever was a widespread belief. It's definitely not a common superstition today, though I wouldn't doubt that there are some people somewhere that believe it. And after eating fruit (like apples or grapes) I certainly feel a distinct difference in the way water feels in my throat, so I can believe this superstition being started or perpetuated.