Never say you know the last word about any human heart! I was once treated to a revelation which startled and touched me in the nature of a person with whom I had been acquainted--well, as I supposed--for years, whose character I had had good reasons, heaven knows, to appreciate and in regard to whom I flattered myself I had nothing more to learn.
The quote used by William Boyd to open his story comes from arguably the master of 19th century literary realism, Henry James Jr. It appears in his short story, 'Louisa Pallant', written in 1888.
American-born but an English citizen by the time of his death in 1916, Henry James was a champion of writing from a first person point of view.