Here’s a brief definition of noir fiction, from Wikepedia.

"Noir fiction is the name sometimes given to a mode of crime fiction regarded as a subset of the hardboiled style. According to noir aficionado George Tuttle,

'In this sub-genre, the protagonist is usually not a detective, but instead either a victim, a suspect, or a perpetrator. He is someone tied directly to the crime, not an outsider called to solve or fix the situation. Other common characteristics...are the emphasis on sexual relationships and the use of sex to advance the plot and the self-destructive qualities of the lead characters. This type of fiction also has the lean, direct writing style and the gritty realism commonly associated with hardboiled fiction.'"

To me, the central element of noir is “the self-destructive qualities of the lead characters,” because they are what drive the plot and create the questions that, when answered, become a story’s messages.

I suspect all of us humans have self-destructive qualities, and as we learn how to see them, we can at least moderate their effects on our lives and on the lives of others.