Major works of literature such as The Glass Menagerie by Tennessee Williams, unlike simple fables or sermons, rarely have singular lessons; in fact, it is precisely their complexity and lack of simplistic moralizing that contributes to their greatness.
The characters in this play are all deeply flawed, especially in their refusal to see current reality clearly and to react to their actual situations in life.
Amanda Wingfield is constantly reliving her past as a southern belle, unwilling to face the fact that the manners, conventions, and habits she learned as a child are not useful skills for a more modern world. Although she does attempt to enroll Laura in a business college, Laura too is fragile and unworldly, crippled by her shyness as well as a childhood illness, to complete her course work or find a job. Ultimately, both women still exist within a traditional mythos of femininity where they are fundamentally passive, taught a sort of learned helplessness and reliance on male generosity. Tom shows how this patriarchal dynamic also traps men in a web of obligations. All of the characters are trapped by the history of their families and of the south.
While some people might take away from this play a belief in the importance of developing career skills to avoid the trap of dependency, others will in a certain way admire the tenacity of Amanda in holding the family together, however tenuously, and see the play as showing how people are cast adrift as the bounds of community fail.