Appendix VI : A few principal rituals – Liber Reguli. 
Magick Book IV : Liber ABA, Part III : Magick in Theory and Practice (1929) 
Context: We know one thing only. Absolute existence, absolute motion, absolute direction, absolute simultaneity, absolute truth, all such ideas: they have not, and never can have, any real meaning. If a man in delirium tremens fell into the Hudson River, he might remember the proverb and clutch at an imaginary straw. Words such as "truth" are like that straw. Confusion of thought is concealed, and its impotence denied, by the invention. This paragraph opened with "We know": yet, questioned, "we" make haste to deny the possibility of possessing, or even of defining, knowledge. What could be more certain to a parabola-philosopher that he could be approached in two ways, and two only? It would be indeed little less that the whole body of his knowledge, implied in the theory of his definition of himself, and confirmed by every single experience. He could receive impressions only be meeting A, or being caught up by B. Yet he would be wrong in an infinite number of ways. There are therefore Aleph-Zero possibilities that at any moment a man may find himself totally transformed. And it may be that our present dazzled bewilderment is due to our recognition of the existence of a new dimension of thought, which seems so "inscrutably infinite" and "absurd" and "immoral," etc. — because we have not studied it long enough to appreciate that its laws are identical with our own, though extended to new conceptions.
                                    
“All we know of the truth is that the absolute truth, such as it is, is beyond our reach.”
De Docta Ignorantia (On Learned Ignorance) (1440)
Help us to complete the source, original and additional information
Nicholas of Cusa 49
German philosopher, theologian, jurist, and astronomer 1401–1464Related quotes
                                        
                                        Truth, ii 
The Note-Books of Samuel Butler (1912), Part XIX - Truth and Convenience
                                    
                                        
                                        Encyclical Fides et Ratio, 14 September 1998 
Source:  www.vatican.va http://www.vatican.va/holy_father/john_paul_ii/encyclicals/documents/hf_jp-ii_enc_14091998_fides-et-ratio_en.html
                                    
1990s, Memoirs (1995)
                                        
                                        Introduction "On The Sources of Knowledge and of Ignorance" Section XVII, p. 30 Variant translation: I believe it is worthwhile trying to discover more about the world, even if this only teaches us how little we know. It might do us good to remember from time to time that, while differing widely in the various little bits we know, in our infinite ignorance we are all equal.
If we thus admit that there is no authority beyond the reach of criticism to be found within the whole province of our knowledge, however far we may have penetrated into the unknown, then we can retain, without risk of dogmatism, the idea that truth itself is beyond all human authority. Indeed, we are not only able to retain this idea, we must retain it. For without it there can be no objective standards of scientific inquiry, no criticism of our conjectured solutions, no groping for the unknown, and no quest for knowledge. 
Conjectures and Refutations: The Growth of Scientific Knowledge (1963)
                                    
                                        
                                        Notes, 1962; as cited on  collected quotes on the website of Gerhard Richter: 'on Art' https://www.gerhard-richter.com/en/quotes/art-1 
1960's
                                    
Source: The Magnificent Defeat (1966)