"It's tough, him getting it like that. Miles had his faults same as the rest of us, but I guess he must've had some good points too."
"I guess so," Spade agreed in a tone that was utterly meaningless, and went out of the alley. (2.46)
The fact that Miles was murdered in a seemingly senseless way suggests that death can come at any time. We have no way of controlling when or how we die, and in this sense, we lack a certain amount of free will since there's no way of avoiding death.
"He felt like somebody had taken the lid off life and let him look at the works." (7.13)
When Flitcraft narrowly misses being killed by a falling beam, he feels as if good luck was the only thing that prevented him from dying. The total randomness of death not only terrifies Flitcraft, but makes him completely alter the course of his life.
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. He, the good citizen-husband-father, could be wiped out between office and restaurant by the accident of a falling beam. He knew then that men died at haphazard like that, and lived only while blind chance spared them. (7.14)
Flitcraft believes that men have no free will in a world where blind chance is the only thing that determines whether you live or die. In an attempt to adjust to the haphazardness of death, Flitcraft leaves his current life and travels around the country, but he eventually picks up where he left off and remarries a woman remarkably similar to his first wife. What does this say about fate and human nature that Flitcraft returns to the same routine he left behind?
Life could be ended be ended for him at random by a falling beam: he would change his life at random by simply going away […] He wasn't sorry for what he had done. It seemed reasonable enough to him. I don't think he even knew he had settled back naturally into the same groove he had jumped out of it Tacoma. But that's the part of it I always liked. He adjusted himself to beams falling, and then no more of them fell, and he adjusted to them not falling. (7.15)
The part about the Flitcraft parable that appeals most to Spade is the idea that the dream Flitcraft is chasing is also the life he once led. Why does Flitcraft go back to his former lifestyle? Why does this resonate so strongly with Spade?
"I know what I'm talking about. I've been through it all before and expect to go through it again. At one time or another I've had to tell everybody from the Supreme Court down to go to hell, and I've got away with it. I got away with it because I never let myself forget that a day of reckoning was coming. I never forget that when the day of reckoning comes I want to be all set to march into headquarters pushing a victim in front of me, saying: 'Here, you chumps, is your criminal!' As long as I can do that I can put my thumb to my nose and wriggle my fingers at all the law in the book." (18.33)
Spade tries to get away with a lot of things throughout the novel. Sometimes he's lucky, sometimes he's able to control situations so that they fall to his advantage. But he's also aware that at some point, his "day of reckoning" will come when he'll no longer be able to fool fate. It is inevitable that he'll eventually have to face the consequences of his actions.