Final answer:
Stanley destroys Blanche's plans for her future by exposing her lies and destroying her self-worth, leading to her mental breakdown in 'A Streetcar Named Desire'.
Step-by-step explanation:
Stanley, in Tennessee Williams' play A Streetcar Named Desire, destroys Blanche's plans for her future by aggressively undermining her sense of self-worth and by exposing the lies she has constructed around her past and her present.
Stanley's relentless investigation into Blanche's history and his eventual revelation of this to those around her strips Blanche of the persona she has created. As a result, he shatters the illusions that she desperately clings to for her self-preservation and hope for a better future. His actions are significant because they lead to Blanche's mental breakdown and loss of any potential security or happiness she might have had.