Characterize Sam Spade.

Probably Sam Spade's chief characteristic is skepticism. He never quite believes in the genuineness of the fabulous black bird, so he is not really surprised or disappointed when the one he gets from Captain Jabobi turns out to be a fake. Spade is a realist. He has an extremely cynical attitude about people. He demonstrates this characteristic in Chapter 12 when he goes to see his lawyer Sid Wise. Spade had sent Iva Archer to him in order to find out what she had been doing on the night of her husband Miles' murder. Spade expected Wise to reveal everything she told him in confidence, and Wise told him everything Iva had told him about her night.

Sam's face was expressionless. He asked: "You believe her?"
"Don't you?" Wise replied.
"How do I know? How do I know it isn't something you fixed up between you to tell me?"
Wise smiled. "You don't cash many checks for strangers, do you, Sammy?"
"Not basketfuls."

Spade can hardly trust his own lawyer when he knows that Wise will violate his ethical obligation to Iva Archer by divulging everything she told him. Both Spade and Wise believe that you can't trust anybody. It is because Spade doesn't trust anybody that he stays out of the troubles that Brigid O'Shaughnessy is trying to cause him. In the end he tells her he is going to have her sent to San Quentin for murdering his partner Miles Archer. When she pleads with him and stresses her love for him, he says:

"I should trust you? You who arranged that nice little trick for—for my predecessor, Thursby? You who knocked off Miles, a man you had nothing against, in cold blood, just like swatting a fly, for the sake of double-crossing Thursby?: You, who double-crossed Gutman, Cairo, Thursby—one, two, three? You who've never played square with me for half an hour at a stretch since I've known you? I should trust you? No, no, darling. I wouldn't do it even if I could. Why should I?"

Spade has many women in his life, including Iva Archer, but he lives alone in a San Francisco efficiency apartment and sleeps in a Murphy bed. He is likely to remain alone for the rest of his life.