Loneliness is the poverty of self; solitude is richness of self.

The aphorism hinges on a moral-psychological contrast. “Loneliness” names an experience of lack: the self feels diminished, cut off, and unable to draw sustenance from within—hence “poverty of self.” “Solitude,” by contrast, is chosen and generative; it implies a self sufficiently stocked with attention, memory, imagination, and purpose to make aloneness fertile—“richness of self.” Sarton elevates solitude from mere absence of company to a condition of inward abundance, suggesting that the difference is not external circumstance but the quality of one’s relationship to one’s own mind and life. The line also implicitly defends the artist’s need for privacy and sustained reflection.