Blanche's distortion of reality is a coping mechanism she uses to survive, and at the heart of her having to use a coping mechanism is desire (the title of the play, of course) and the discrepancy between how Southern women are expected to act, and how they do and must act.
When she distorts reality by insisting that her former male friend is going to come and rescue her, she is attempting to cope with her situation and to hold on to her dignity. As a woman in a patriarchal society, she is forced to rely on men for all of the things a person needs to survive. Blanche cannot be herself. Stanley can fulfill his desires, and so can Stella. Blanche cannot. Society won't allow it. When Mitch discovers that she is not the ideal, virginal-like maiden he thought she was and rejects her, and when Stanley rapes her and is in the process of getting away with it, Blanche attempts to hold on to her dignity by insisting at least one man still thinks her worthy of attention. Of course, her attempts are futile. Stella believes Stanley and takes his side, and Stanley wins the battle for Stella that he an Blanche have been fighting. Blanche is hauled away.
Blanche does what she can to survive and to hold on to her sanity and her dignity.
Blanche went spiraling down when three major life-changing events came almost one after another, leaving her in limbo without knowing how or why it all happened.
The first was discovering her husband (whom she loved immensely) in bed with another man. Blanche could not bear it, and undestandably so. She thought she could shrug it off and move on- but she couldn't.
The second was her husband's sucicide. Given that Blanche was unable to shake off what she saw, she went out with the men (her husband and her lover) and, in a daze of alcohol she exploded. She told him "You make me sick", and this prompted his shooting himself. She carried that throughout the play, whenever the lights hit, and the music begins.
The third was the loss of Belle Reeve. No matter what anyone says, money CAN provide some comfort from stress and pain. She lost that too. When her father began to get sick already Stella had gone off to marry, and it was Blanche who stayed behind letting it all go and not knowing how to fix it.
All these things happened in a way that nobody saw coming. Blanche was not psychologically nor socially prepared to handle the situations. Her world, as she knew it, was removed from under her feet, and she became numb- only that, instead of moving above and beyond the problem, she succumbed to her inner demons: alcohol, sex, and debauchery.
Blanche is the epitome of the broken woman: One whose situation is so desperate that her former self dies and a new one has to be made up from the shambles in which she fell.
This is the most fundamental question to come out of the play. I think that anyone who reads it is left with answering this fundamental question. In my mind, I would say that Blanche's own experiences help to distort her perception of reality. It seems to me that to understand Blanche and why things appear the way they are to her is to grasp her full experience. Her childhood, the structure that helped to provide meaning to her, is officially gone. The South has transformed itself from a traditional based, agrarian outfit to one that mirrors the North, complete with industrialization and a fluid social order where definitions are not clear. To have her entire childhood and formative years erased and seemingly the values that go along with it is jarring. When Blanche hurriedly and almost frantically enters a room with men and says to them not to get up and must face the words of, "Don't worry, we won't," it speaks volumes as to how the world and her conception of it has changed. One of the values that she grew up with is the notion of a woman getting married and following the traditional lifestyle within domesticity. Blanche tried this and, for all purposed, failed. Her marriage to a man who was presumably gay had seismic impacts upon her. I would look to lines in the play to see how Blanche describes her first husband. You will notice that the delicate nature of language is not only because of the topic matter, but also because of the very idea that her freedom has turned out to be a failure in this realm. There was no handbook to help guide Blanche in this domain, and this further enhances her distortion of the world. Finally, I would say that the futile exercise of freedom is brutal to Blanche. In no way does this absolve her of responsibility for what happened, but it does explain why she views reality in the way that she does. Blanche feels cursed with the fact that her freedom, her initiatives, have not materialized. This helps to bring out the fact she has to almost deny reality a bit because to constantly witness one's acts of freedom doomed to futility or uselessness is painful. To see hope quashed at every turn takes a toll on one's soul. Blanche represents the painful end of what it mean to be human: To try and to fail. This might be why Williams seeks to have the audience "pity" Blanche, a character who is meant to remind us of our own youth and challenges within it. In the end, all of these converge to distort Blanche's reality.