The quote reflects on the challenges of finding stability and meaning in life, suggesting that many people may only experience an imperfect or flawed existence, represented by the "false arch." This metaphor emphasizes the absence of a vital element, or keystone, that would otherwise bring completion and support to one's life structure.

In this context, the "keystone" symbolizes the rare moments of fulfillment or understanding that some individuals are fortunate enough to discover. Stegner's words encourage readers to consider the complexities of life and the often significant obstacles that hinder their pursuit of true contentment.