“Enduring Love” by Ian McEwan (post 7): Why does explicitly psychiatric novel ignore symptoms of multiple personality in two characters?

As previously noted, this novel concludes with a fictitious article from a fictitious journal of psychiatry that discusses this novel from a psychiatric point of view, as if the characters were real people. It is the author’s own psychiatric analysis of this novel.

The author’s psychiatric analysis ignores symptoms suggestive of multiple personality in two major characters: the protagonist saw himself from a distance, and the villain addressed an “invisible presence” (see prior posts).

Evidently, the author did not see these as psychiatric symptoms. Why?

Because these may be the kinds of things that he, himself (and other people who may have multiple personality trait) might experience, and he (and those others) are not crazy.