“Pain will force even the truthful to speak falsely.”
Maxim 232
Sentences, The Moral Sayings of Publius Syrus, a Roman Slave
Help us to complete the source, original and additional information
Publilio Siro 112
Latin writerRelated quotes

“To speak falsely is the mark of a slave, but the truth is noble.”
to Euphrates, Epp. Apoll. 83
Letters

“Better to know the quick pain of truth than the ongoing pain of a long-held false hope.”
Source: Voice of the Gods

Literary and Historical Miscellanies (1855), The Necessity, the Reality, and the Promise of the Progress of the Human Race (1854)
Context: No science has been reached, no thought generated, no truth discovered, which has not from all time existed potentially in every human mind. The belief in the progress of the race does not, therefore, spring from the supposed possibility of his acquiring new faculties, or coming into the possession of a new nature.
Still less does truth vary. They speak falsely who say that truth is the daughter of time; it is the child of eternity, and as old as the Divine mind. The perception of it takes place in the order of time; truth itself knows nothing of the succession of ages. Neither does morality need to perfect itself; it is what it always has been, and always will be. Its distinctions are older than the sea or the dry land, than the earth or the sun. The relation of good to evil is from the beginning, and is unalterable.

Verse 17.
To Demonicus
Context: Guard yourself against accusations, even if they are false; for the multitude are ignorant of the truth and look only to reputation. In all things resolve to act as though the whole world would see what you do; for even if you conceal your deeds for the moment, later you will be found out. But most of all will you have the respect of men, if you are seen to avoid doing things which you would blame others for doing.

“One voice, speaking truth is a greater force than fleets and armies, given time; plenty of time.”
Source: Hainish Cycle, The Left Hand of Darkness (1969), Chapter 3 “The Mad King” (p. 27)

“The dead may speak the truth only, even when it discredits themselves.”
The Golden Fleece (1944), Invocation.
General sources