“There is no royal road to learning; no short cut to the acquirement of any art.”

μὴ εἶναι βασιλικὴν ἀτραπὸν ἐπί γεωμετρίαν, Non est regia [inquit Euclides] ad Geometriam via
Reply given when the ruler Ptolemy I Soter asked Euclid if there was a shorter road to learning geometry than through Euclid's Elements.The "Royal Road" was the road built across Anatolia and Persia by Darius I which allowed rapid communication and troop movement, but use of ἀτραπός (rather than ὁδός) conveys the connotation of "short cut".
The Greek is from Proclus (412–485 AD) in Commentary on the First Book of Euclid's Elements, the Latin translation is by Francesco Barozzi, 1560) the English translation follows Glenn R. Morrow (1970), p. 57 http://books.google.com/books?id=JZEHj2fEmqAC&q=royal#v=snippet&q=royal&f=false.
Attributed

Source: The Interpretation of Dreams

Feeling
The Note-Books of Samuel Butler (1912), Part VI - Mind and Matter

From The Great Judge by Philip Hamburger (1946).
Extra-judicial writings

The Book of My Life (1930)
Context: My father, in my earliest childhood, taught me the rudiments of arithmetic, and about that time made me acquainted with the arcana; whence he had come by this learning I know not. This was about my ninth year. Shortly after, he instructed me in the elements of the astronomy of Arabia, meanwhile trying to instill in me some system of theory for memorizing, for I had been poorly endowed with the ability to remember. After I was twelve years old he taught me the first six books of Euclid, but in such a manner that he expended no effort on such parts as I was able to understand by myself.
This is the knowledge I was able to acquire and learn without any elementary schooling...<!--Ch. 34

The Interpretation of Dreams (1900), from The Standard Edition of the Complete Psychological Works of Sigmund Freud, translated by James Strachey.
At any rate the interpretation of dreams is the via regia to a knowledge of the unconscious in the psychic life.
Alternate translation by Abraham Arden Brill, p. 483 http://books.google.com/books?id=OSYJAAAAIAAJ&pg=PA483#v=onepage&q&f=false. Freud did use the Latin phrase via regia in the original as opposed to translating it into the German of the surrounding text.
"Royal road" or via regia is an allusion to a statement attributed to Euclid.
1900s

The Books in My Life (1952) Preface (2nd edition. New York: New Directions Publishing, 1969, p. 12)

Source: The Life of Poetry (1949), p. 150
Context: The continuity of film, in which the writer deals with a track of images moving at a given rate of speed, and a separate sound-track which is joined arbitrarily to the image-track, is closer to the continuity of poetry than anything else in art. But the heaviness of the collective work on a commercial film, the repressive codes and sanctions, unspoken and spoken, the company-town feeling raised to its highest, richest, most obsessive-compulsive level in Hollywood, puts the process at the end of any creative spectrum farthest from the making of a poem.
At the same time, almost anything that can be said to make the difficulties of poetry dissolve for the reader, or even to make the reader want to deal with those "difficulties," can be said in terms of film. These images are like the action sequences of a well-made movie — a good thriller will use the excitement of timing, of action let in from several approaches, of crisis prepared for emotionally and intellectually, so that you can look back and recognize the way of its arrival; or, better, feel it coming until the moment of proof arrives, meeting your memory and your recognition.
The cutting of films is a parable in the motion of any art that lives in time, as well as a parable in the ethics of communication.

"Self-Culture", an address in Boston (September 1838)
Context: The path to perfection is difficult to men in every lot; there is no royal road for rich or poor. But difficulties are meant to rouse, not discourage. The human spirit is to grow strong by conflict. And how much has it already overcome! Under what burdens of oppression has it made its way for ages What mountains of difficulty has it cleared! And with all this experience, shall we say that the progress of the mass of men is to be despaired of; that the chains of bodily necessity are too strong and ponderous to be broken by the mind; that servile, unimproving drudgery is the unalterable condition of the multitude of the human race?