It is the experience or permontition of that loneliness, perhaps, that drives a lot of young writers into this search for rules. I envy musicians very much, myself. They get to play together, their art is largely communal; and there are rules to it, an accepted body of axioms and techniques, which can be put into words or at least demonstrated, and so taught. Writing cannot be shared, nor can it be taught as technique, except on the most superficial level. All a writer’s real learning is done alone, thinking, reading other people’s books, or writing — practicing. A really good writing class or workshop can give us some shadow of what musicians have all the time — the excitement of a group working together, so that each member outdoes himself — but what comes out of that is not a collaboration, a joint accomplishment, like a string quartet or a symphony performance, but a lot of totally separate, isolated works, expressions of individual souls. And therefore there are no rules, except those each individual makes up for himself.
LeGuin is not talking about the rules of grammar or spelling; those are the plumbing and electrical work in the house. She's talking more about architecture, décor, location-location-location — all the things for which there is no actual codified rule set, but just raw experience that has to be experienced.
Every writer of significance is their own island, and you have to go to their work and come back on your own. Likewise, you make your own island with your work, and you have to learn how to bring people to it — and how to leave it and come back to it as well.
I find I like the solitary part of writing a lot more rewarding than the social part of it. I don't like hassling other people about how great my work is, because most people don't want to hear about it anyway. They want to have the pleasure of bumping into it for themselves, so they think it was their idea all along. But a certain amount of that is inevitable. It's just not the main mission, and maybe I expend more energy than I ought to on avoiding it.