While Carrie is the honeypot round which all the flys buzz, ultimately the study of Hurstwood is the focus of the novel: an almost scientific study of the middle-aged man in Western society.
Of course the phenomenon of 'middle age crisis' has become virtually passé since the '70s film
Middle Age Crazy with Bruce Dern and Ann Margret. (Doesn't appear to be on DVD...)
http://www.amazon.com/Middle-Age-Cra...0179438&sr=1-1
**SPOILER ALERT**
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But Dreiser's study of Hurstwood is more like 'middle age stupid', as he ruins his own life for a taste of sweet young Carrie; proceeding then as he further ages to make mistake after mistake (incipient Alzheimers?) leading unto poverty, destitution, and suicide.
Really it's a terrifying study of alienation and decay (moral, mental, physical).
Although I must say, Hurstwood is a much more sympathetic character than Clyde in
An American Tragedy, who commits an horrifically brutal crime against an innocent person.
Incidentially, the main characters of
The Financier and
The Genius are both marginally modeled on Frank Lloyd Wright.
http://www.amazon.com/Frank-Lloyd-Wr...0180232&sr=1-1