It's honestly all over the place, which is what keeps it interesting for me. A lot of books go the 'study and discipline' route where the power comes from years of memorizing incantations and understanding the underlying principles—like in 'The Name of the Wind'. The magic feels earned and has rules, which I appreciate. But then you have the opposite, where power is a bloodline thing or a gift from some entity; it's less about work and more about destiny or inheritance. That can be fun too, especially when the character has to deal with the responsibility of power they didn't necessarily 'deserve'.
Personally, I lean towards the slow-burn, scholarly mages. There's a satisfaction in seeing them piece together knowledge, fail a few times, and finally pull off a spell through sheer grit. The 'chosen one' trope gets old fast unless it's subverted really well. I'm way more invested in a librarian who cracks an ancient code than a farmboy who discovers he's the lost prince of magic.