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).