“Search not to find what lies too deeply hid,
Nor to know things, whose knowledge is forbid.”

Source: The Crossing

Flowers for Algernon (1966)
Context: Don't misunderstand me," I said. "Intelligence is one of the greatest human gifts. But all too often a search for knowledge drives out the search for love. This is something else I've discovered for myself very recently. I present it to you as a hypothesis: Intelligence without the ability to give and receive affection leads to mental and moral breakdown, to neurosis, and possibly even psychosis. And I say that the mind absorbed in and involved in itself as a self-centered end, to the exclusion of human relationships, can only lead to violence and pain.

Source: Anam Cara: A Book of Celtic Wisdom

Written on the Bedchamber Door of Charles II, as quoted in The Book of Days : A Miscellany of Popular Antiquities (1832) by Robert Chambers, Viol. II, July 26, p. 126.

Source: Broca's Brain (1979), Chapter 23, “A Sunday Sermon” (pp. 339-340)

A Mathematician Grappling With His Century (2001). Quoted in slide no.22 https://edpolicy.stanford.edu/sites/default/files/events/materials/elgw-boaler-ppt.pdf
Context: I was always deeply uncertain about my own intellectual capacity; I thought I was unintelligent. And it is true that I was, and still am, rather slow. I need time to seize things because I always need to understand them fully. Even when I was the first to answer the teacher's questions, I knew it was because they happened to be questions to which I already knew the answer. But if a new question arose, usually students who weren't as good as I was answered before me. Towards the end of the eleventh grade, I secretly thought of myself as stupid. I worried about this for a long time. Not only did I believe I was stupid, but I couldn't understand the contradiction between this stupidity and my good grades. I never talked about this to anyone, but I always felt convinced that my imposture would someday be revealed: the whole world and myself would finally see that what looked like intelligence was really just an illusion. If this ever happened, apparently no one noticed it, and I’m still just as slow. (...)At the end of the eleventh grade, I took the measure of the situation, and came to the conclusion that rapidity doesn't have a precise relation to intelligence. What is important is to deeply understand things and their relations to each other. This is where intelligence lies. The fact of being quick or slow isn't really relevant. Naturally, it's helpful to be quick, like it is to have a good memory. But it's neither necessary nor sufficient for intellectual success.

Science and Immortality (1904)
Context: The search of science for the spirits has been neither long nor earnest; nor is it a matter of surprise that it has not been undertaken earlier by men whose training had fitted them for the work.
It is no clear, vasty deep, but a muddy, Acheronian pool in which our modern spirits dwell, with Circe as the presiding deity and the Witch of Endor as her high priestess. Commingling with the solemn incantations of the devotees who throng the banks, one can hear the mocking laughter of Puck and of Ariel, as they play among the sedges and sing the monotonous refrain, "What fools these mortals be!" Sadly besmirched, and more fitted for a sojourn in Ancyra than in Athens, has been the condition of those who have returned from the quest, and we cannot wonder that scientific men have hesitated to stir the pool and risk a touch from Circe's wand. All the more honour to those who have with honest effort striven to pierce the veil and explore the mysteries which lie behind it.

Death of the Flowers http://www.bartleby.com/248/85.html (1832), st. 4, lines 23-24

This Business of Living (1935-1950)