An author's ability to solve conflict satisfactorily with magic is directly proportional to how well the reader understands said magic.
I'll admit that when I started writing this blog post, I had forgotten the rest of the essay in which Sanderson lays out his argument for this principle (linked above). He actually makes allowances for authors writing different styles of magic than he prefers. But his scale runs from "soft" magic (i.e. little or no explanation in the story) to hard magic (i.e. the rules are given and followed within the story). I'd come to this topic inspired by a conversation in the Books thread over at NarniaWeb about logical vs. intuitive stories. I've recently read a couple of books that seemed to work in stark contrast to Sanderson's First Law, and I thought perhaps the logical vs. intuitive distinction might be relevant to why I was drawn to those books. In Uprooted, the magic is certainly arrayed in such a light. Angieszka's magic is very intuitive or instinctual compared to the magic of the other wizards in the book. Her ability to (and insistence on) creating magic that feels right as opposed to following strictures of academic thought baffles and chagrins every other wizard she meets.
But I thought that logical vs. intuitive didn't quite sit right in both Uprooted and Mary Robinette Kowal's Ghost Talkers, there is a logic to the magic. (To use Sanderson's scale, I'd say Uprooted is 60-75% soft magic, while Ghost Talkers is more in the middle at 50-50.) The difference with these two is that the logic, the rules of the magic, aren't integral to the story. They are window dressing, a vehicle for other things, such as meditations on the meaning of love and the nature of courage. So I asked myself what really differentiated the magic in these two books (and others like The Lord of the Rings that never quite reveal the workings of magic, even in the expanded world of The Silmarillion and other posthumous publications) from the books Sanderson is talking about (and writing). That led me to the idea of implicit vs. explicit magic.
In my mind, implicit magic is magic whose rules are rarely if ever laid out in a systematic way. You may understand the principles behind it (i.e. love is the most powerful magic) but you'll never get a Sanderson-level treatise on the physics of the magic. That sort of thing belongs to explicit magic, the sort of system where it is a system, and one the reader can understand almost as well as the characters and the author do.
Having reread Sanderson's essay, I'm not sure my categorization is greatly different from his soft vs. hard magic. The one advantage I see in mine is the loss of an implied snobbishness that seems to creep in with distinctions of hard and soft. I don't think Sanderson intends this (he says in the essay he enjoys reading books across the spectrum), but it's there. When science fiction is discussed, hard sci-fi (utilizing only known scientific principles and their extrapolations) tends to get more credit, as though it is superior to soft sci-fi (Star Trek, etc.) on some essential level. Regardless of whether Sanderson intends this sort of superior mindset, it is bound to the terms he uses. The fact that he prefers to write hard magic systems only makes plain his own bias.
I don't want this to sound as though I am trash-talking Sanderson. I admire him as an author and I've enjoyed his books that I've read. But I do think his first law is slightly flawed. It assumes (or at least heavily implies) that his is the better way to write magic, neglecting many books of similar calibre.
Personally, I tend to write books which are in the realm of the implicit. Even when I have a magic system, I don't usually spell out (pun intended) all the mechanisms of the magic. While I can appreciate the type of story that does this, I tend to care more about getting the characters from point A to point B and seeing what happens along the way. There are moments where explicit magic is called for in almost any fantasy story, but if there's anything my recent experiences with Uprooted and Ghost Talkers has taught me, it's that implicit magic--stories that focus on wonder rather than workings--speak to me as a writer and a reader more deeply than explicit magic. And I don't want to see those stories viewed as "less than" their counterparts across the shelf. Just different. Perhaps quieter in some ways, but no less skillful for their different path.