I would be inclined to restate the theme as: In order to succeed one must take risks. Or: Nothing ventured, nothing gained. Sam Spade is the only character who succeeds, and he takes lots of risks. He must enjoy risk-taking, since he is having an affair with the wife of his own partner. He risks getting shots when he takes Joel Cairo's gun away. He risks getting shot by Wilmer. He risks getting arrested, and he even risks getting convicted of the murder of either Miles Archer or Floyd Thursby. When he tells Brigid the story about Flitcraft, he suggests that life itself is a continual risk. You never know from one day to the next what might happen to you. This is illustrated by the entire novel. A pretty woman comes to Spade's office for help, and all of a sudden he is up to his neck in troubles.