Douglas Adams (2016). “Dirk Gently's Holistic Detective Agency Box Set: Dirk Gently's Holistic Detective Agency and The Long Dark Tea-Time of the Soul”, p.354, Simon and Schuster
Attributed to Aristotle in Diogenes Laertius "The Lives and Opinions of Eminent Philosophers" translated by C. D. Yonge and Henry G. Bohn (p. 188), 1853.