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

May Sarton (1912-1995) Belgian-American poet, novelist, memoirist [pen name of Eleanore Marie Sarton]

Mrs. Stevens Hears the Mermaids Singing (1965)
    (Source)

Repeated in an interview with John McNally, Castaway's Choice, KCRW (1 Jul 1988).