“I'm a slave to this leaf in a diary that lists what I must do, what I must say, every half hour.”

Journal entry, Gilleleie (1 August 1835) Journals 1A; this is considered to be one of the earliest statements of existentialist thought.
Variant translation: My focus should be on what I do in life, not knowing everything, excluding knowledge on what you do. The is key to find a purpose, whatever it truly is that God wills me to do; it's crucial to find a truth which is true to me, to find the idea which I am willing to live and die for.
Later variant: What I really lack is to be clear in my mind what I am to do, not what I am to know, except in so far as a certain knowledge must precede every action. The thing is to understand myself, to see what God really wishes me to do: the thing is to find a truth which is true for me, to find the idea for which I can live and die. … I certainly do not deny that I still recognize an imperative of knowledge and that through it one can work upon men, but it must be taken up into my life, and that is what I now recognize as the most important thing.
Later expression of such thoughts in a letter to Peter Wilhelm Lund (31 August 1835)
Variant translation: I must find a truth that is true for me.
1830s, The Journals of Søren Kierkegaard, 1830s
Context: What I really need is to get clear about what I must do, not what I must know, except insofar as knowledge must precede every act. What matters is to find a purpose, to see what it really is that God wills that I shall do; the crucial thing is to find a truth which is truth for me, to find the idea for which I am willing to live and die.

J. Agee, trans. (1989), p. 64
Das Geheimherz der Uhr [The Secret Heart of the Clock] (1987)

Beverley Lyons and Lee-Ann Fullerton (February 28, 2004) "The Razz: Jimmy's Brent on being funny", The Daily Record.

Celebetty: Heath Ledger: The Patriot Interview http://www.beatboxbetty.com/celebetty/heathledger/heathledger.htm, about his role in The Patriot, published at BeatBoxBetty.com (2000).
Variant: I'm not good at future planning. I don't plan at all. I don't know what I'm doing tomorrow. I don't have a day planner and I don't have a diary. I completely live in the now, not in the past, not in the future.

Source: Ghost Town

Speech at the University of Las Villas (1959)

Source: Earthsea Books, The Farthest Shore (1972), Chapter 4, "Magelight" (Ged)

"Sermon From the Savoy", New Musical Express (29 September 1984)
Context: I'm terribly intuitive—I always thought I was intellectual about what I do, but I've come to the realisation that I have absolutely no idea what I'm doing half the time, that the majority of the stuff that I do is totally intuitive, totally about where I am physically and mentally at any moment in time and I have a far harder time than anybody else explaining it and analysing it. That's the territory of the artist anyway: to be quite at sea with what he does, and working towards not being intuive about it and being far more methodical and academic about it.