In A Streetcar Named Desire it is certain that the character of Blanche does depend on the fantasies and lies that she tells herself in order to build her persona. Unfortunately for Blanche, the lies that she tells herself are so far from her reality that the only thing that she has been able to build from them is the very shallow, empty shell of a broken woman.
Blanche, no longer a young, successfully married and financially capable woman, relies on the vestiges of her looks to try to build something permanent out of charming unintelligent men. In her case, she has her eyes set on Mitch, not because he loves him, but because she figures that he could help her gain back some dignity, respectability and, who knows, maybe he could even provide her with a home where she can hide from the rest of the world.
However, Blanche builds an entirely fake world for Mitch to see; she claims to be virtuous, courteous, dignified, and conservative. She rejects his advances to create an atmosphere of prudishness that is as juxtaposed to Blanche's real self as can be. Moreover, Blanche has come to make herself believe that the mistakes from her past could never come back to haunt her. Little does he believe in the power of the "word to mouth" folks who learn about each other and create legends out of people who clearly show instability. Out of all unstable people, Blanche certainly can take the top spot.
Therefore, the appearance that Blanche wants to show to the world: her impeccable clothing, her knowledge of sophisticated things, her charm and her mannerisms, are merely feeble decorations that go outside the shell of a very empty individual. With her demeanor and behavior, Blanche has created a fantasy where she is a good, high-society woman. In reality, Blanche is a failure. Her nature, and circumstances, have continuously shown her how little she can actually accomplish in a world that is way more intelligent than she is. In the end, her lies will all be discovered and she will, literally, disappear along with the image of Blanche that she intended the world to see, and believe in.