How does Edith Wharton show the readers that Lily Bart was responsible for her own end in The House of Mirth?

Every chapter of The House of Mirth presents one more more situations in which the character of Lily Bart is juxtaposed to a diatribe that requires either immediate action, or preparation. The lack of action and lack of preparation that we consistently see coming from Lily's part are partly responsible for the events that she ends up experiencing. In chapter 2, Lily is described for doing this very thing. Her social circle says that Lily is someone who 

works like a slave preparing the ground and sowing her seed; but the day she ought to be reaping the harvest she over-sleeps herself or goes off on a picnic

Therefore, lack of action and lack of initiative are the two demons that bring Lily down, and which she needs to fight against.

Just to name some examples, here are some things that Lily could have done, but just never did in the novel:

• She refuses to engage in Dorsett's plan to expose Bertha, who humiliated her. 


• She refuses to pay attention to Rosedale when she had a chance


• She refuses to settle for Selden because he is not rich


• She misses her chance to impress Percy Gryce 


• She is unable to plan her expenses ahead


• She is not willing to give up a certain expectation of luxury in her life

It is only in the end that she finally learns her lesson and becomes more proactive about life, even paying off her debt right before her end comes. 

However, if we revert back to chapter 3 of the novel, we get a good insight as to why Lily is the way that she is. In chapter 3, Wharton explains that Lily was 19 years-old when she had to "revisit her view of the universe." Lily finds out the hard way that her family has come to financial ruin in a way so fast that it shocks her.  From living in a busy, sophisticated and elegant home, she now has to learn to live without those luxuries. The shock may have been so intense, and her upbringing so devoid of reality, that even as an adult Lily cannot manage to put her life together. 

...she was not made for mean and shabby surroundings, for the squalid compromises of poverty. Her whole being dilated in an atmosphere of luxury; it was the background she required, the only climate she could breathe in.

Luxury and beauty were part of there imprinting. She was born that way, raised that way, and encouraged to remain that way. It was impossible for her to act differently; she had a tremendous weakness of character when it came to the trappings of society, and she was too inactive and unwilling to learn from the cues to do anything productive about it. Therefore, Lily is a victim of herself and her circumstances. Still, she could have avoided a lot of her own pain if she had only taken a proactive and sensitive approach.