“Since knowledge is but sorrow's spy,
It is not safe to know.”
The Just Italian (licensed Oct. 2, 1629; printed 1630), Act v. Sc. 1.
Compare: "From ignorance our comfort flows", Matthew Prior, To the Hon. Charles Montague; "Where ignorance is bliss, ’T is folly to be wise", Thomas Gray, Eton College, Stanza 10.
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William Davenant 3
English poet and playwright 1606–1668Related quotes

“Our times are still not safe and sane enough
for faces to show ordinary sorrow.”
"Smiles"
Poems New and Collected (1998), A Large Number (1976)
Context: The going's rough, and so we need the laugh
of bright incisors, molars of goodwill.
Our times are still not safe and sane enough
for faces to show ordinary sorrow.
“And as every spy knows, common enemies are how allies always begin.”
Source: Don't Judge a Girl by Her Cover
Watchman. Somewhere here, there is the question of "seeing clearly". Seeing what? According to what?
Book A (sketchbook), c 1965: as quoted in Jasper Johns, Writings, sketchbook Notes, Interviews, ed. Kirk Varnedoe, Moma New York, 1996, p. 60
1960s

“In much wisdom is much grief: and he that increaseth knowledge increaseth sorrow.”
Ecclesiastes, 1:18 http://bible.cc/ecclesiastes/1-18.htm, King James Version
Source: Think (1999), Chapter One, Knowledge, p. 17
“Since human knowledge is not perfect, a more knowledgeable person is not always right.”
Why I Am a Muslim: And a Christian and a Jew (2020)
“We can't spy on them if they aren't spying on us, now can we?" Warped logic, but okay.”
Source: Alice in Zombieland