“If you are wise, mingle these two elements: do not hope without despair, or despair without hope.”
Alternate translation: Hope not without despair, despair not without hope. (translated by Zachariah Rush).
Source: Epistulae Morales ad Lucilium (Moral Letters to Lucilius), Letter CIV: On Care of Health and Peace of Mind, Line 12
Original
Si sapis, alterum alteri misce: nec speraveris sine desperatione nec desperaveris sine spe.
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Seneca the Younger 225
Roman Stoic philosopher, statesman, and dramatist -4–65 BCRelated quotes

“None without hope e'er lov'd the brightest fair,
But love can hope where reason would despair.”
Epigram; reported in Bartlett's Familiar Quotations, 10th ed. (1919).
“It's not the despair, Laura, I can stand the despair. It's the hope.”
Clockwise (1986), cited from Malcolm Page File on Frayn (London: Methuen, 1994) p. 65.

“2542. Hope is as cheap as Despair.”
Introductio ad prudentiam: Part II (1727), Gnomologia (1732)

“Despair exists only when there is hope.”
11th Public Talk, London, UK (25 May 1961)
1960s

“Prayer is a bridge from despair to hope.”
Too Busy Not to Pray (2008, InterVarsity Press)

“My only hope lies in my despair.”
Mon unique espérance est dans mon désespoir.
Atalide, Bajazet, (1672), act I, scene IV.