In his introduction to The Maltese Falcon, Dashiell Hammett wrote the following:
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.
Sam Spade is not the ideal man, and still less is he the perfect gentleman, but he is the ideal detective: supremely good at his job and emotionally and intellectually adapted to the demanding work he has to do. Most importantly, he is no fool. His pragmatic attitude to life extends to his relationships with women. Spade has seen plenty of men, including his partner, Miles Archer, making fools of themselves over women, and he is determined never to be one of them.
At the end of The Maltese Falcon, Spade thinks that he may be in love with Brigid O'Shaughnessy. He has the opportunity to play the romantic hero and save her, at some risk to himself. Instead, he reminds himself that he is under no moral obligation to help Brigid. She killed his partner and has repeatedly lied to him. He therefore turns her in to the police, telling her that he refuses to be a "sap." His cold-blooded attitude shocks the other principal woman in Spade's life, his secretary, Effie Perine:
Her voice was queer as the expression on her face. "You did that, Sam, to her?"
He nodded. "Your Sam's a detective." He looked sharply at her. He put his arm around her waist, his hand on her hip. "She did kill Miles, angel," he said gently, "offhand, like that." He snapped the fingers of his other hand.
She escaped from his arm as if it had hurt her. "Don't, please, don't touch me," she said brokenly. "I know—I know you're right. You're right. But don't touch me now—not now."
Sam Spade has sexual relationships with women when the opportunity arises. He may even fall in love with them in his own reserved way. However, he always retains a certain hardheaded emotional distance. Effie finally understands him well enough to realize that the only possible relationship a woman can have with him must involve a certain amount of emotional detachment and self-interest.