In the Agatha Christie book Five Little Pigs, Hercule Poirot deduces that one of the suspects had recently read The Moon And Sixpence by W Somerset Maugham but it is never explained how. So... how?
I know this isn't really very helpful, it's been a long time since I read the book but the most annoying thing about Agatha Christie is the way she always saves the best clues for the last few pages. Her detective has all the answers so the reader can't solve the mystery by themselves, the only thing I can suggest is re-reading the book with your dilemma in mind.