Our language has wisely sensed the two sides of being alone. It has created the word "loneliness" to express the pain of being alone. And it has created the word "solitude" to express the glory of being alone.
(Paul Tillich, 1886-1965)

Loneliness is the poverty of self, solitude is the richness of self.
(May Barton, 1912-1995)

In solitude, where we are least alone.
(Lord Byron, 1788-1824)

All men's miseries derive from not being able to sit quiet in a room alone.
(Blaise Pascal, 1623-1662)

Those who know the value and the exquisite taste of solitary freedom (for one is only free when one is alone)...
(Isabelle Eberhardt, 1877-1904)