Raymond Chandler's Private Detective

As Raymond Chandler himself would later admit, the typical real life private detective was not as he imagined his protagonist Philip Marlowe, an intellectual whose idea of a good time was a quiet night at home with a bottle of rye and a book of chess problems. The real PI was an ex-cop with the brains of a turtle who spent his time finding out where people had moved to. [In reality, Chandler had no knowledge whatsoever regarding private investigators, criminal investigation, criminal law, or policing. He was a novelist with no background or training in such matters. His ignorance shows up in his plots which are thin, literary, and unrealistic.] 

John Baxter, A Pound of Paper, 2003