A system is all about limits. Whether we’re doing hard or soft magic, we must still decide on limits unless we genuinely want an all-powerful being. There are arguably two kinds of limits: those imposed by the universe/gods and those caused by mortals. For the latter, this means that someone has devised a system of magic on our world.
For example, the arch wizard Kier discovered and developed a series of spells now known as Kierzadry. Another wizard called Taria invented Tariandry. Both had their talents, knowledge, inventiveness, research ability, and access to materials with which to experiment. They also ran into problems, solving some and not others, and deciding they’d found a limit (whether true or not) to one thing or another. And they built on their work over possibly decades, crafting spells that considered their learning. The result is two different schools of magic (or types), each with their own rules.
Let’s say Kier lived with varied landscapes nearby, with unique wildlife and plants, like the Amazon on Earth. It’s likely his spells use exotic materials, and maybe gestures or magic words are lesser parts of his spells. But Taria lived in a desert city when none of that was available, so her spells rely much more on words and gestures. Maybe she even contacted spirits, demons, or the like, and these supernatural forces are part of what she developed. Do we need to explain any of this to the audience? No, but imagining the origin of a magic type helps us develop it and use the natural limits of the physical world to define it.
Maybe those who practice Kierzardy are very good at the manipulation of materials but struggle to perform Tariandry due to the complex gestures and words, and lack skill in contacting spirits, who might be unfamiliar with them and therefore reluctant to answer. A Kierzardist might subsequently imagine this is another limit and wrongly tell others Tariandry can’t be done by them. A Tariandist might decide that it’s difficult to get the materials needed to perform Kierzardry, even at stores, and that even once acquired, processing them in the correct way is too much like cooking with rare materials that they don’t understand. It’s also possible that these are rival schools of magic and practitioners generally refuse to teach each other. The last thing they want is someone who’s adept at both.