W. H. Auden, I think it was, said “Poetry, after all, makes nothing happen.” Except, of course, that it does. Hemingway’s fiction shaped how a century saw masculinity and femininity, power and powerlessness, choice and weakness. People made decisions, changed their lives, and acted differently because of Hemingway, but in no way that could be quantified or predicted. Similarly, when I do a spell for — let’s say — money, I am causing change in the world, but in no way that I can predict. I only know that the outcome is likely to be that I’ll get money from an unexpected source. I don’t know how or why.
Obviously, in the case of literature, the chain of cause and effect is clear from retrospect, or at least, clear-ish. The chain of cause and effect in magic is less clear. Maybe I do a spell, and it makes spirits do something that causes me to get money. Or maybe I do a spell, and it makes some sort of magical energy move and do something. It’s always that chewy nougat center that our magical theories are trying to fill.