Why does Sue Grafton gratuitously suggest that a character in S is for Silence might have multiple personality?

After my recent posts about Sue Grafton, I decided to read one of her novels, which I had not done for many years. So I just read S is for Silence (2005), which I had never read.

Tom Padgett is described as a man who, with his wife Cora out of town, “was an entirely different man. It was like having a separate personality, one he called forth and wore like a smoking jacket while she was gone. He had two such personalities, as a matter of fact. When he drank, especially at the Blue Moon, he relaxed into the blue-collar type from which he sprang. He was a good old boy at heart. He liked his boots and jeans, adding a western-cut sport coat when he felt like dressing up. Here in Cora’s fancy house, sober and unobserved, he activated another side of his nature, playing the Lord of the Manor. He was jaunty and dapper. He used a cigarette holder when he smoked and affected a snooty accent when he talked to himself.”

The information that this character has more than one personality is neither a clue nor a red herring in this mystery novel. It is gratuitous. There is no reason for its inclusion.

When a novel includes multiple personality for no literary reason, I think the reason is that the author takes multiple personality for granted. It is simply how people are, in that author’s personal experience.