The quote reflects on the complex nature of human emotions compared to simple, straightforward concepts like a line or a street. While physical things can be undeniably straight, it suggests that the human heart is inherently intricate and not bound by such simplicity.
Tennessee Williams uses this metaphor to highlight that our feelings and experiences have many twists and turns, akin to a winding road through mountains. This complexity emphasizes the depth of human relationships and emotions in contrast to the straightforwardness of physical forms.