Discuss the respective self-deceptions in "The Glass Menagerie". How do these, as Tom says, illustrate a "truth" about life?

The self-deception that exists for the Wingfield family is illustrated in the conflict of illusion vs reality.  For Amanda Wingfield, who lives in her memories more than in the present, she deludes herself into believing that she was the belle of the ball in her days as a girl in Blue Mountain.  Over and over again, she tells the story of how she had seventeen gentleman callers in one day.  Yet, somehow, she can't explain, fully, why she picked Mr. Wingfield.  It is hard to understand why she would have picked him, since she had the pick of the sons of plantation owners.

Laura's deception is that she prefers to remain in her fantasy world rather than the real world.   The evidence of this is when she deceives her mother into believing that she is attending Rubicam's Business College, when in fact she stopped going weeks ago and actually spends her days wandering around going to museums, and zoos.  Amanda wants Laura to learn office skills so that she can get a job and support herself, but Laura does not have the confidence, determination or maturity to stay in the program.  She suffers from terrible anxiety and can't handle the pressure.

Tom, who works at a shoe warehouse, a deadend job, probably the best one he could get, he is not very motivated, he appears to be disconnected from life, uninterested.  Although he claims to long for adventure, and imagines himself a writer, he is really a bitter, angry young man, who resents his father for abandoning the family and leaving the burden on his shoulders.  The truth is that he can't wait to abandon his mother and sister in the same way, and he does.

Tom also does not take the time or respect the nature of his mother's request for him to bring a gentleman caller home for Laura.  He does not mention that he has a sister to Jim O'Connor, had he been honest, Jim would have had no choice but to reveal that he was engaged. 

The deception that Tom enacts on Amanda is too much for her, she wants him to leave at the end of the play.  After he does not pay the light bill, and the lights go out during dinner, Amanda is left, along with Laura in the darkness.  Tom has plunged his sister and mother into emotional and physical darkness, walking out on them and never looking back.