The House of Mirth's opening chapters provide a great example of how the novel pays attention to behavioral details. In a train station, Selden carefully analyzes Lily with the intent of determining why she is there. He then plays a mind game on her, walking past her to see if she greets him or tries to hide from him. This analysis of actions is typical in the novel, as seen later on when Lily and George Dorset are assumed to be having an affair after they are seen alone together at night in a train station. And, of course, Selden becomes enraged at Lily when he sees her leaving the house of Gus Trenor late one night by herself.
Given that money is the controlling factor in Lily's life, to what can it lead? There are essentially two possibilities in The House of Mirth (and any novel of manners): acceptance/marriage or exile/death. Perhaps the most enjoyable way to read the novel is to begin reading with the belief that the book could go either way: Lily could get married and succeed, or fail and die. In this case, it is the latter option that happens. How does Wharton work toward that end? With each chapter, particularly in Book Two, the factors of bad luck and social instability combine to slowly remove Lily from society: bad luck because Lily was with the wrong man at the wrong time in France, and social instability because Lily was not entrenched enough in society for her word to be respected over that of Bertha.