“Worried thought prevents practical thought which could prevent worried thought.”

After hearing that his brother John F. Kennedy had been assassinated in Dallas, TX, on 22 November 1963, as reported https://books.google.com/books?id=nsOlkJ7yVhMC&q=I+thought+they%27d+get+one+of+us%2C+but+Jack%2C+after+all+he%27s+been+through%2C+never+worried+about+it+I+thought+it+would+be+me.#v=snippet&q=%22I%20thought%20they%27d%20get%20one%20of%20us%22%20%22but%20Jack%2C%20after%20all%20he%E2%80%99d%20been%20through%2C%20never%20worried%20about%20it....%20I%20thought%20it%20would%20be%20me.%22&f=false by Ed Guthman in Peter Collier & David Horowitz's The Kennedys: An American Drama https://www.google.com/search?tbo=p&tbm=bks&q=intitle:%22The+Kennedys%22+inauthor:%22David+Horowitz%22+inauthor:%22Peter+Collier%22&num=50 (1984), ISBN 1893554317, p. 249

Preface
The Right to Be Happy (1927)
Context: It has taken us centuries of thought and mockery to shake the medieval system; thought and mockery here and now are required to prevent the mechanists from building another. Without falling into a mystical vitalism that reverences organic nature as sacred, we can at least try rather to serve than to subdue the prancing seas of life. With this in view I have taken as impulses, instincts, or needs certain driving forces in the human species as we know it at present, and argued for such social and economic changes as will give them new, free, and varied expression. To take even this first step towards a happy society is a herculean task. After it has been accomplished, generations to come will see what the creature will do next. We none of us know; and we should be thoroughly on our guard against all those who pretend that they do.

Knowing Yourself: The True in the False (1996)

Source: PTI Me and my family know the truth: Sania http://articles.economictimes.indiatimes.com/2010-04-03/news/27587127_1_siddiquis-pakistani-cricketer-shoaib-malik-sania-mirza, The Economic Times, 3 April 2010

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.

Ma pensée, c'est moi: voilà pourquoi je ne peux pas m'arrêter. J'existe parce que je pense … et je ne peux pas m'empêcher de penser.
Lundi ("Monday")
Nausea (1938)

Source: The Thief