But nevertheless Chris Routledge in The Guardian writes about Hammett's--perhaps very few--digressions:
On a related note, I just read Hammett's Thin Man a few months back and totally recommend it for if you're into hard-boiled detective fiction. After all, next to Raymond Chandler, he is the master of the hard-boiler.
By reputation Hammett is a writer of tough, pared-down prose and ought not to be associated with digression. His detective novels are plot-driven and fast-paced, with an A to B momentum that barely lets up. His audience in the 1920s and 1930s, mostly the readers of pulp magazines such as Black Mask, were not looking for philosophy when they went to the newsstand in the morning. They did their reading for entertainment, not enlightenment.
Yet as literary digressions go the Flitcraft parable is near perfect: it is completely unexpected, forcefully significant in an oblique kind of way, and beautifully formed. In the three pages or so in which Sam Spade tells Brigid O'Shaughnessy the story of Flitcraft, who "left his real-estate office, in Tahoma, to go to luncheon one day and never returned", we are presented with a glimpse of Spade's hard-boiled world view and a little treatise on the arbitrariness of life. Like O'Shaughnessy we are left baffled by it.