The Helmers' marriage is doomed to failure because of the deception woven into their daily lives, but this is a direct result of Nora's lack of options due to the society she lives in.
Most obviously, Nora has deceived her husband regarding their finances. When he becomes ill, she knows that he would never finance the treatment himself, so she secures the money while lying to him about the source:
Torvald, will all his masculine pride—how painfully humiliating for him if he ever found out he was in debt to me. That would just ruin our relationship. Our beautiful, happy home would never be the same.
Nora's intentions are good. She has made sacrifices along the way to repay this debt and has always kept the truth from her husband in order to spare his pride. Yet she realizes that this deception could be the end of their marriage. However, what other options does a woman in this time period have? She isn't allowed to work, own property, or handle her own finances. Her deception is based on her desperation.
Nora has also had to commit forgery in order to finance the trip that saves her husband's health. Because Krogstad knows this, he tries to blackmail her into obtaining a good job for him with Nora's husband:
I'll tell you what. I want to recoup,Mrs. Helmer; I want to get on in the world—and there's where your husband can help me. For a year and a half I've kept myself clean of anything disreputable—all that time struggling with the worst conditions; but I was satisfied, working my way up step by step. Now I tell you, I want to move on. I want to get back in the bank—in a better position. Your husband can set up a job for me . . .
Krogstad uses his masculinity to threaten Nora's marriage, blackmailing her about her secret forgery. Again, Nora finds herself trapped by the lack of possibilities for women living in her society.
Nora is deceptive, but her intentions are good, and had women been given more rights, she would have had more options to consider. She made the best possible choices for her family and herself given the limited opportunities before her. The play shows that desperation sometimes drives people to make deceptive choices.
Deception, both legal and moral, is everywhere in A Doll's House. Almost every character in the play is affected by it to some extent. The greatest deception of all, of course, is Nora's self-deception in relation to her marriage. She's been playing the part of dutiful wife to Torvald, all the while being kept in a state of arrested development by a man who thinks of her as little more than a child. It's only much later on in the play when Nora realizes that her marriage is a total sham and that she'll never be able to realize her true self, unless she summons up the courage to stop living a lie and leave her old life behind for good.
Ironically, it is an act of deception in the legal sense of the word that leads directly to Nora's epiphany, to her abandonment of self-deception. This, of course, is a reference to Nora's forging of her late father's signature on a loan application. Krogstad was in on the fraud, but he has finally faced up to the role he played in the deception and wants Nora to acknowledge her role in it too. Yet she can't— not initially, at any rate. At this point in the play, Nora's still firmly in the grip of self-deception. Technically, she may have broken the law, but she only did it out of love for her husband.
But the financial deception gives Nora a brief glimpse of what life could be like outside the stifling confines of the doll's house Torvald has constructed for her. For probably the first time in her life, she's acted independently, on her own initiative, and now there's no going back. Her participation in an act of fraud has provided the catalyst for her recognition of the fundamentally fraudulent nature of her marriage.
Deception is the foundational basis of A Doll's House. Nora practices deception to save Torvald's life through money gained from a loan to which she deceptively signs her father's name. She continues her daily deceptions inherent in paying back the money. she deceives on large and small things, such as the macaroon cookies. Dr. Rank practices deception in maintaining his friendship with Torvald while secretly in love with Nora and with Nora by acting the friend when his feelings are deeper. Torvald practices deception in his role with Nora, acting like a loving husband but in reality putting values of honor and pride ahead of her.
Each instance of deception is motivated by different feelings or purposes. Nora's initial deception was motivated by her husband's illness with the purpose being to save his life. Her continued deceptions are motivated by the need to repay the loan and the taste of independence and freedom that the whole incident opened up to her. Dr. Rank's deception is motivated by the bounds of honor--it is dishonorable to love your friend's wife--and by his deep love for Nora. He has a double purpose: to be loyal to Torvald and to be near Nora. Torvald's deception is motivated by a character flaw that values honor and pride above human and family relationships. His purpose is to have a lovely wife and a lovely life with all the appearances of propriety, moderation, and pride that he values.