A belief, however necessary it may be for the preservation of a species, has nothing to do with truth. The falseness of a judgment is not for us necessarily an objection to a judgment. The question is to what extent it is life-promoting, life-preserving, species preserving, perhaps even species cultivating. To recognize untruth as a condition of life--that certainly means resisting accustomed value feelings in a dangerous way; and a philosophy that risks this would by that token alone place itself beyond good and evil.
What makes a belief true or false I call a "fact." The particular fact that makes a given belief true or false I call its "objective," and the relation of the belief to its objective I call the "reference" or the "objective reference" of the belief. Thus, if I believe that Columbus crossed the Atlantic in 1492, the "objective" of my belief is Columbus's actual voyage, and the "reference" of my belief is the relation between my belief and the voyage--that relation, namely, in virtue of which the voyage makes my belief true (or, in another case, false). "Reference" of beliefs differs from "meaning" of words in various ways, but especially in the fact that it is of two kinds, "true" reference and "false" reference. The truth or falsehood of a belief does not depend upon anything intrinsic to the belief, but upon the nature of its relation to its objective. The intrinsic nature of belief can be treated without reference to what makes it true or false.
-Bertrand Russell, The Analysis of Mind, Lecture XII. Belief
As soon as you begin to believe in something, then you can no longer see anything else. The truth you believe in and cling to makes you unavailable to hear anything new.
-Pema Chödrön, The Wisdom of No Escape
The effectiveness of a doctrine does not come from its meaning but from its certitude. No doctrine however profound and sublime will be effective unless it is presented as the embodiment of the one and only truth…
If a doctrine is not unintelligible, it has to be vague; and if neither unintelligible nor vague, it has to be unverifiable. One has to get to heaven or the distant future to determine the truth of an effective doctrine. When some part of a doctrine is relatively simple, there is a tendency among the faithful to complicate and obscure it. Simple words are made pregnant with meaning and made to look like symbols in a secret message. There is thus an illiterate air about the most literate true believer. He seems to use words as if he were ignorant of their true meaning.
-Eric Hoffer, The True Believer: Thoughts on the Nature of Mass Movements, pp. 80-81, 1951