The quote is taken from Mark Twain's notebook, 1898.

An earlier version of his observation appears in his novel, A Connecticut Yankee in King Arthur's Court. This refers to eyes — to PERCEPTION rather than judgement.

Then I seemed to see a row of black dots appear along that ridge — human heads? I couldn't tell; it mightn't be anything at all; you can't depend on your eyes when your imagination is out of focus.

When our PERCEPTION is more focused, and its scope is wider, both our senses and our judgements can better align with our actual EXPERIENCE.

As beliefs and dreams inform our actions, these then change what reality becomes, but because actions, and inaction initiate cascades of reactions it's impossible accurately to predict their result. Inescapably we are part of a whole and that then limits our ability to "effectively chart our own paths".

Human beings are spatially and temporally limited parts of the whole that we call "universe"; yet we experience ourselves and our feelings as separate from the rest, a kind of optical delusion of our consciousness.

As often quoted, Newton's Law states that, For every action there is an equal and opposite reaction.

At least up until 2015, billionnaire, Richard Branson's thoughts on Mark Twain's words were widely reported, for instance by Quote Investigator

It is a natural human instinct to want to know what lies before us. By dreaming and imagining, we can effectively chart our own paths. As Mark Twain pointed out "You can't rely on your eyes when your imagination is out of focus." It is therefore crucial that we put our imagination in focus, so that we can realize opportunities and act on them to reach our goals, and in turn move the world forward.

This quote, as at 14 February 2026, from Branson's post, My three favorite quotes on imagination, dated 13 October 2014, was recorded here; however, the references provided there, on Quote Investigator and elsewhere, only redirected to his blog on the Virgin website, where no information on it was available.

footnotes of n_Einstein_Translation.php included in entryNote.php, e_Einstein_HumanDelusion.php, and e_personalMeta.php.

Ein Mensch ist ein räumlich und zeitlich beschränktes Stück des Ganzen, was wir „Universum“ nennen. Er erlebt sich und sein Fühlen als abgetrennt gegenüber dem Rest, eine optische Täuschung seines Bewusstseins. Das Streben nach Befreiung von dieser Täuschung ist der einzige Gegenstand wirklicher Religion. Nicht das Nähren der Illusion sondern nur ihre Überwindung gibt uns das erreichbare Maß inneren Friedens.    Albert Einstein, 1950.

Einstein wrote the above (bold emphasis added), in ink, in a note now held in the Albert Einstein Archives, Jerusalem. The edit I have made  is of the translation, written in another hand, that appears underneath them. 

There were several reasons for editing that translation — to reflect the gender neutrality of the German more consistently; to echo Einstein's use of the words, delusion, and, illusion;  and to better reflect the certitude of the note's opening argument, carried in the brevity of the German yet somehow absent in the translation on the note itself. In the end, the edit below, supported by translations by Google on 6 March 2024, is only a minor edit of it:

Human beings are spatially and temporally limited parts of the whole that we call "universe"; yet we experience ourselves and our feelings as separate from the rest, a kind of optical delusion of our consciousness. The striving to be free of this delusion is the only object of real religion. It is not nurturing the illusion but only overcoming it which gives that measure of inner peace which is attainable.    Albert Einstein, 1950.

The translation, in pencil on the original note, became the text of the condolence letter sent from Einstein to Dr. Marcus on 12 February 1950. The first two sentences of it were then used to open the letter of condolence sent on the 4 March 1950 to Norman Salt.

A human being is a part of a whole, called by us "Universe", a part limited in time and space. He experiences himself, his thoughts and feelings as something separated from the rest — a kind of optical delusion of his consciousness. The striving to free oneself from this delusion is the one issue of pure religion, not to nourish the delusion but to try to overcome it is the way to reach the attainable measure of peace of mind.

delusions and illusions

Einstein spoke the refined German of the Bildungsbürgertum, a language characterized by its precision. It might the be reasonable to assume, as an inspection of Einstein's note also suggests, that his use of the word Täuschung (delusion) twice and Illusion once, was considered not careless.

 The German word Täuschung in the original note, meaning 'delusion' (JPG opens in a new tab).

Etymologically the word delusion implies an action, a deceiving, referring here to that suffered by human beings through our consciousness, through which we perceive a deceptive appearance, the illusion of being "separated from the rest".

Technically, delusion is a belief that, though false, has been surrendered to and accepted by the whole mind as a truth; illusion is an impression that, though false, is entertained on the recommendation of the senses or the imagination. Illusion (n.), developed in Church Latin from the late 14c. onwards to mean: a "deceptive appearance".

Although I believe that translations I have found are faithful to the originals, stripped of their context, quotations can lose much of their quality. Transliteration of punctuation, for instance, can result in an English that makes their authors sound coarse or uneducated; and 'grammatical transliterations' may substitute gender bias for the gender neutrality in an original.

Where I have edited translations it has been only in order to address issues of punctuation, prosody, and inference, that I found detracted from the content of the originals. The edits have been made with due diligence, and although I am not a professional translator or writer, I believe they are faithful, and required to make the fluency, erudition, and sensibility of the originals explicit — original texts are provided so readers may draw their own conclusions.

Footnote {delusion01a} of n_Einstein_Translation.php.

..as free-spirited and anti-bourgeois as Einstein may have appeared to be all his life, his language remained the refined German of the Bildungsbürgertum of his time, a language he mastered with virtuosity.