Entire quote is Harrison's writing advice:
Once I start, I very rarely change my mind about the nature of the story. And when I begin writing, it’s sound that guides me—language, not plot. Plot can be overrated. What I strive for more is rhythm. When you have the rhythm of a character, the novel becomes almost like a musical composition. It’s like taking dictation, when you’re really attuned to the rhythm of that voice.
You can’t go to it. It has to come to you. You have to find the voice of the character. Your own voice should be irrelevant in a novel. Bad novels are full of opinions, and the writer intruding, when you should leave it to your character.
When you’re not writing in the first person as the speaking character, the danger is there’s too much temptation to show off. And many writers do. They hit what they think is a high note, then keeping shooting for that. I like what Deborah Treisman at The New Yorker says: She has to have a story, she can’t just have effect. There must be more than writerly effect. And it’s true. Nobody likes a showoff.
So, you learn to think like the character, to speak with them. Wolf’s structure grew out of that rhythm more than any conventional sense of plot. In the case of my novel Dalva, I felt I could dream the character. It’s like you have an extra voice in your brain while you’re writing. And it’s a wonderful feeling, though it doesn’t happen often.