The Sanderson school of hard magic systems seems so ever present right now in fantasy, maybe I should spend some time discussing soft magic systems and how much they can strengthen stories and make them more impactful

The most famous story with soft magic is of course, The Lord of the Rings. You'll notice that nobody really talks about the magic in LOTR the way we would with Sanderson's allomancy or Rothfuss' sympathy. The magic of the Ring fades into the background, and highlights the themes

Trauma and the effect of carrying an emotional weight or burden on the mind and heart is a big theme in LOTR, and the effects of the Ring are meant to enhance that creeping, despairing weightiness. Even some of the other magic elements in the series imply heavy tolls and dangers

The main argument against soft magic systems is that you can't use them to solve plot problems if your rules aren't defined. You create deus ex machina moments otherwise, where the hero can pull out a magic whatever that was never mentioned and save the day. It kills tension

But that's fine. Instead, you can use soft magic to create powerful character/psychological moments. In writing there are external(plot) and internal(character) conflicts. Hard magic is great for external conflict, but can undermine the message in an internal conflict

Emotional and psychological conflicts do not always follow a definable set of rules. Anyone struggling with mental illness can speak to the truth of that. In using soft magic systems without defined rules, you can use it to affect the characters without cheapening their struggles

But you don't have to keep your soft magicky stuff confined to your heroes feelings and emotional baggage. You can define harder parts of your system without losing that wondrous soft magic feel of anything's possible

Harry Potter is an extremely popular example of a soft magic system. While there appears to be a spell for almost anything, Harry is limited to only the spells he has learned, and those spells are introduced and defined as needed. But it doesn't feel like deus ex machina

But it allows the heroes to solve plot problems as well as communicate themes with the magic system. You don't have to write a textbook for your magic system and its limitations, as long as you handle it carefully and with a little foresight

You'll also notice that it becomes easier to write soft magic when your POV character is a non-magical character(see Tolkein again, and Game of Thrones). Your magic and world can maintain that huge and unknowable feel, because your readers have no extra access to magic knowledge

But in my experience, writing a magic-user in soft magic can be fun for similar reasons if you write a novice. They grasp the basics and can solve a handful of problems, and maybe they're unusually talented, but then they encounter weird and terrifying shit they can't fathom