“The insight process flows smoothly if sensual desires do not arise. If they do arise, however, they obstruct the flow of insight. They appear as rivals to insight, as if saying, "It is our turn; stay away insight!"”

Source: The Fabric of the Cosmos: Space, Time, and the Texture of Reality

Internet Encyclopedia of Philosophy

Source: The Bed of Procrustes: Philosophical and Practical Aphorisms (2010), p. 84

... (een flits van inzicht) komt nooit vanzelf, in de zin dat je er geen moeite voor hoeft te doen. Je moet je er echt wel voor inspannen. Er is een mooi spreekwoord voor: “toeval schiet de voorbereide geest te hulp”.
Zo’n inzicht komt wel toevallig, maar je krijgt het alleen als je bent voorbereid. Het inzicht komt niet vanzelf.
In Interview with Professor Carlo Beenakker. Interviewers: Ramy El-Dardiry and Roderick Knuiman (February 1, 2006).

On Mind and Thought (1993), p. 34
Posthumous publications
Context: It is astonishingly beautiful and interesting, how thought is absent when you have an insight. Thought cannot have an insight. It is only when the mind is not operating mechanically in the structure of thought that you have an insight. Having had an insight, thought draws a conclusion from that insight. And then thought acts and thought is mechanical. So I have to find out whether having an insight into myself, which means into the world, and not drawing a conclusion from it is possible. If I draw a conclusion, I act on an idea, on an image, on a symbol, which is the structure of thought, and so I am constantly preventing myself from having insight, from understanding things as they are.

Source: Lateral Thinking : Creativity Step by Step (1970), p. 5; Preface.
Context: Lateral thinking... is the process of using information to bring about creativity and insight restructuring. Lateral thinking can be learned, practised and used. It is possible to acquire skill in it just as it is possible to acquire skill in mathematics.

A Testament (1957)

Essay as "Mr. X" (1969)
Context: When I'm high I can penetrate into the past, recall childhood memories, friends, relatives, playthings, streets, smells, sounds, and tastes from a vanished era. I can reconstruct the actual occurrences in childhood events only half understood at the time. Many but not all my cannabis trips have somewhere in them a symbolism significant to me which I won't attempt to describe here, a kind of mandala embossed on the high. Free-associating to this mandala, both visually and as plays on words, has produced a very rich array of insights.
There is a myth about such highs: the user has an illusion of great insight, but it does not survive scrutiny in the morning. I am convinced that this is an error, and that the devastating insights achieved when high are real insights; the main problem is putting these insights in a form acceptable to the quite different self that we are when we're down the next day.

Quotes, NYU Speech (2004)
Context: Our founders were insightful students of human nature. They feared the abuse of power because they understood that every human being has not only "better angels" in his nature, but also an innate vulnerability to temptation — especially the temptation to abuse power over others.
Our founders understood full well that a system of checks and balances is needed in our constitution because every human being lives with an internal system of checks and balances that cannot be relied upon to produce virtue if they are allowed to attain an unhealthy degree of power over their fellow citizens.