Honestly, I've seen multiple takes on what "magic" is; with some people describing it in more traditional terms (spells, hexes, potions, etc), and others basically saying, "it's any time action A seems to lead to outcome B, but the mechanism is unknown". The latter I'm fine with and actually encourage, because tbh, the physical world is fucking weird.

There's so much we don't know about physics that putting some cool rocks and a stick in a letter and mailing it to a friend might legitimately bring them good fortune, either because you've improved their mood (most likely), leading their brain to being more positive and efficient, or maybe something you did in the process happened to kickstart a row of dominos that happened to bring them good fortune. It doesn't really matter that you don't know the exact step that caused it, just that one of the steps seemed to do it and that's fine.

I suppose you could take a scientific approach to it though and study what exactly you did and how it seemed to effect the outcome of your magic. Who knows, might stumble across a new scientific law in the process.

On a side note regarding horoscopes, I don't believe in them except that I sometimes wonder if they're the result of patterns, which then became self-fullfilling prophecies. Astrologer notices that X happens more often when A is high in the sky and B is near the horizon, and predicts the occurrence of X. X occurs and people believe the astrologer. Next time A is high in the sky and B is near the horizon, the astrologer once again predicts X, and the people, as part of their belief, unintentionally cause X to happen again. Same thing with Chinese birth years. I wonder if it's the result of people noticing patterns in society and then laymen misattributing it to magic.