Like most of Dashiell Hammett's detective characters, Sam Spade is a man with no specific past, just a job to do and an amoral code of ethics that drives him to get it done. Hammett himself said:
"Spade has no original. He is a dream man in the sense that he is what most of the private detectives I worked with would like to have been and in their cockier moments thought they approached. For your private detective does not or did not ten years ago when he was my colleague want to be an erudite solver of riddles in the Sherlock Holmes manner; he wants to be a hard and shifty fellow, able to take care of himself in any situation, able to get the best of anybody he comes in contact with, whether criminal, innocent by-stander or client."
Unlike Hammett's most frequently used character, the unnamed "Continental Op," Spade works for himself, does not always get along with the police, and appears to have some appeal for the opposite sex.
In the novel, Sam Spade gives us an unintentional insight into himself (and, some have suggested, into Hammett) during a lengthy parable narrated to Brigid O'Shaughnessy (AKA Wonderly and LaBlanc). He tells her about a case he was hired to investigate - the disappearance of a man called Flitcraft. Flitcraft had been a respectable middle class husband and father, but one day abandoned his wife in Tacoma without explanation. Spade finds Flitcraft in Spokane, where he has a new wife and a very similar life to the one he left in the previous city. He explains to Spade that he had a moment of revelation the day he left when walking to lunch, as a large steel girder fell from a construction site and nearly killed him:
"He was more shocked than really frightened. He felt as if someone had taken the lid off his life and let him look at the works."
Spade says that Flitcraft realized that he had been "a good citizen and a good husband and father, not by any compulsion, but simply because he was a man who was most comfortable in step with his surroundings...The life he knew was a clean, orderly, sane, responsible affair. Now a falling beam had shown him that life was fundamentally none of these things...What disturbed him was the discovery that in sensibly ordering his affairs he had got out of step, and not into step, with life." The irony, Spade explains, is that, after coming to this moment of self-understanding, Flitcraft had wandered off to "find himself," only to return to a life very much like the one he abandoned. "He adjusted himself to beams falling, and then no more of them fell, and he adjusted himself to their not falling." For Sam Spade, life is a kind of con-game, which each person plays on him- or herself, and moments of transcendant understanding are only momentary jogs in a machine which otherwise functions almost completely on automatic.