Magic should be something that is fundamentally different from the mundane. You can observe it, and you can poke at it, and you can figure out that certain kinds of poking produce a consistent effect that can be used to your advantage. But nobody actually knows what's going on and how it works.
Which is why warlock is the main spellcasting class in my setting, followed by druids. Mortal magic ultimately comes from spirits, and what exactly spirits are is unclear. (The only other spellcasting class are bards, which work mechanically as always, but are priests who are calling on divine spirits for their enchantments and illusions.)
Magic items are commonly physical remains of magical creatures that still hold some of the creature's power. Some are always active, others need to get a nudge by someone who can feel magic to release their power. Sometimes they work immediately as they are chopped off the original creature, but the process of creating magic items is really mostly modifying remains to make it possible to activate their powers when desired. How their power really works and where it actually comes from remains a mystery to the creator.