A World of Winds
The multiverse has a fundamental reality to it; one inaccessible to anyone except possibly the gods. However, some people have found ways to touch it. Divine casters use the power of greater beings to change it. Arcane casters do it directly, either by some personal power in their blood, developing techniques/secrets, or receiving them as secrets from otherworldly patrons. Various other experts have found ways to touch on it; monks with ki for example. Many times the same effect can be achieved multiple ways, but sometimes you just can’t get there from here.
For most of this age, there was only so much you could do with it. Magic had it’s upper limits and you just couldn’t get incredibly strong effects. Unless you did something special or knew the right secrets. The most widely known was to gain the favor of a small god. Easier said than done. It usually took a major accomplishment, which if you really needed their help, you probably couldn’t do.
The other methods are more murky. According to popular rumor, the priests of Shakken are supposed to be capable of miracles, but are also supposed to conduct human sacrifice. Anything was possible in the Wildwood, you just didn’t get to pick your possibility. The Kromus Clans said their stories sent people into the realm of the gods to come back with boons, but it wasn’t something they were willing to prove. The Kingdom of Kalathos was rumored to harbor an ancient machine-god stuck int he material realm. The Ormward had the Orm. Then there were the undead of Death Valley, the slow death of the Badlands, the lost dragons of the Wyrmlings, and plenty of local tall tales.
Everyone in touch with reality believes in magic. Whether any given method of magic outside of established practice has any merit is a different issue.