“THE HE-ANCIENT: When a thing is funny, search it for a hidden truth
STREPHON: Yes; and take all the fun out of it.”

Source: West with the Night

O único sentido oculto das coisas
É elas não terem sentido oculto nenhum,
É mais estranho do que todas as estranhezas
E do que os sonhos de todos os poetas
E os pensamentos de todos os filósofos,
Que as coisas sejam realmente o que parecem ser
E não haja nada que compreender.
Sim, eis o que os meus sentidos aprenderam sozinhos:—
As coisas não têm significação: têm existência.
As coisas são o único sentido oculto das coisas.
Alberto Caeiro (heteronym), O Guardador de Rebanhos ("The Keeper of Sheep"), XXXIX, trans. Richard Zenith.

Source: Infinity

Source: The Essential Calvin and Hobbes

Book IV, Ch. 19 : Of Enthusiasm (Chapter added in the fourth edition).
Variant paraphrase, sometimes cited as a direct quote: One unerring mark of the love of truth is not entertaining any proposition with greater assurance than the proofs it is built upon will warrant.
As paraphrased in Peter's Quotations : Ideas for our Time (1979) by Laurence J. Peter, p. 500; also in The Demon-Haunted World : Science as a Candle in the Dark (1994) by Carl Sagan, p. 64
An Essay Concerning Human Understanding (1689)
Context: He that would seriously set upon the search of truth, ought in the first place to prepare his mind with a love of it. For he that loves it not, will not take much pains to get it; nor be much concerned when he misses it. There is nobody in the commonwealth of learning who does not profess himself a lover of truth: and there is not a rational creature that would not take it amiss to be thought otherwise of. And yet, for all this, one may truly say, that there are very few lovers of truth, for truth's sake, even amongst those who persuade themselves that they are so. How a man may know whether he be so in earnest, is worth inquiry: and I think there is one unerring mark of it, viz. The not entertaining any proposition with greater assurance than the proofs it is built upon will warrant. Whoever goes beyond this measure of assent, it is plain receives not the truth in the love of it; loves not truth for truth's sake, but for some other bye-end.

Also quoted in Every Day Is Father's Day: The Best Things Ever Said About Dear Old Dad (1989), p. 150
The Business of Life (1949)

Source: Paul Faber, Surgeon (1879), Ch. 31 : A Conscience
Context: God hides nothing. His very work from the beginning is revelation, — a casting aside of veil after veil, a showing unto men of truth after truth. On and on, from fact to fact divine he advances, until at length in his Son Jesus he unveils his very face. Then begins a fresh unveiling, for the very work of the Father is the work the Son himself has to do, — to reveal. His life was the unveiling of himself, and the unveiling of the Son is still going on, and is that for the sake of which the world exists. When he is unveiled, that is, when we know the Son, we shall know the Father also. The whole of creation, its growth, its history, the gathering total of human existence, is an unveiling of the Father. He is the life, the eternal life, the Only. I see it — ah! believe me — I see it as I cannot say it. From month to month it grows upon me. The lovely home-light, the one essence of peaceful being, is God himself.
He loves light and not darkness, therefore shines, therefore reveals. True, there are infinite gulfs in him, into which our small vision cannot pierce, but they are gulfs of light, and the truths there are invisible only through excess of their own clarity. There is a darkness that comes of effulgence, and the most veiling of all veils is the light. That for which the eye exists is light, but through light no human eye can pierce. — I find myself beyond my depth. I am ever beyond my depth, afloat in an infinite sea; but the depth of the sea knows me, for the ocean of my being is God. — What I would say is this, that the light is not blinding because God would hide, but because the truth is too glorious for our vision. The effulgence of himself God veiled that he might unveil it — in his Son. Inter-universal spaces, icons, eternities — what word of vastness you can find or choose — take unfathomable darkness itself, if you will, to express the infinitude of God, that original splendor existing only to the consciousness of God himself — I say he hides it not, but is revealing it ever, for ever, at all cost of labor, yea of pain to himself. His whole creation is a sacrificing of himself to the being and well-being of his little ones, that, being wrought out at last into partakers of his divine nature, that nature may be revealed in them to their divinest bliss. He brings hidden things out of the light of his own being into the light of ours.
But see how different we are, — until we learn of him! See the tendency of man to conceal his treasures, to claim even truth as his own by discovery, to hide it and be proud of it, gloating over that which he thinks he has in himself, instead of groaning after the infinite of God! We would be forever heaping together possessions, dragging things into the cave of our finitude, our individual self, not perceiving that the things which pass that dreariest of doors, whatever they may have been, are thenceforth "but straws, small sticks, and dust of the floor." When a man would have a truth in thither as if it were of private interpretation, he drags in only the bag which the truth, remaining outside, has burst and left.

One Fish Two Fish Red Fish Blue Fish (1960)
Variant: From there to here,
from here to there,
funny things are everywhere.
Source: One Fish, Two Fish, Red Fish, Blue Fish

Source: Man’s Search for Himself (1953), p. 214