Blaise Pascal [1623-1662] rejected the rigorous rationalism of his contemporary Rene Descartes, asserting in his ‘Pensées’  that a systematic philosophy that presumes to explain God and humanity is a form of pride. Like later existentialists, he saw human life in terms of paradoxes.
“When I consider the short duration of my life, swallowed up in the eternity before and after, the little space I fill, and even can see, engulfed in the infinite immensity of space of which I am ignorant, and knows me not, I am frightened, and am astonished at being here rather than there, why now rather than then.”
Soren Kierkegaard [1813-1855] is arguably the founder of modern existentialism.
“My life has been brought to an impasse, I loathe existence.. One sticks one’s finger into the soil to tell by the smell in what land one is: I stick my finger into existence– it smells of nothing. Where am I? What is this thing called the world? Who is it who has lured me into the thing, and now leaves me here? How did I come into the world? Why was I not consulted? How did I obtain an interest in it? Is it not a voluntary concern? And if I am to be compelled to take part in it, where is the director? Whither shall I turn with my complaint?”
Kierkegaard= “It is perfectly true, as philosophers say, that life must be understood backwards. But they forget the other proposition, that it must be lived forwards.”
Lev Shestov distinguishes between people who advocate that ‘man should live in the categories by which he thinks’, which can be called rationalism, and people who advocate that ‘man should think by the categories in which he lives’, which can be called existential excavation. The rationalist path is abstract, up in the air, and feigns a mental overview and instrumental control of the ground which is only plausible in theory, for when put into practice, it crumbles. The existentialist path is concrete, wrestling with deeps which only loom up when we are on the ground. Therefore something is existentially true only if it can be lived.
Kierkegaard= “Life is not a problem to be solved, but a reality to be experienced.”
Proust= “We don’t receive wisdom; we must discover it for ourselves after a journey through the wilderness which no one can make for us, which no one else can spare us.”
Kierkegaard= “I must find a truth that is true for me.. the idea for which I can live or die.”
Laurens Van Der Post= “It is one of the laws of life that new meaning must be lived before it can be known, and in some mysterious way modern man knows so much that he is the prisoner of his knowledge. The old dynamic conception of the human spirit as something living always on the frontiers of human knowledge has gone. We hide behind what we know. And there is an extraordinarily angry and aggressive quality in the knowledge of modern man; he is angry with what he does not know; he hates and rejects it. He has lost the sense of wonder about the unknown and he treats it as an enemy. The experience which is before knowing, which would enflame his life with new meaning, is cut off from him. Curiously enough, it has never been studied more closely. People have measured the mechanics of it, and the rhythm, but somehow they do not experience it.”
Kao-Feng= “The whole world is a fire pit. With what attitude of mind can you avoid being burnt?”
Camus= “I don’t want to believe death is a door to some other life. For me it is the final dirty adventure.”
Kierkegaard= “Deep within every human being there still lives the anxiety over the possibility of being alone in the world, forgotten by God, overlooked among the millions and millions in this enormous household. A person keeps this anxiety at a distance by looking at the many round about who are related to him as kin and friends, but the anxiety is still there, nevertheless, and he hardly dares think of how he would feel if all this were taken away.”
Nietzsche= “Our age is an agitated one, and precisely for that reason not an age of passion; it heats itself up constantly because it feels that it is not warm– basically it is freezing.. In our times it is merely by means of an echo that events acquire their ‘greatness’– the echo of a newspaper.”
John Macquarrie= “In our everyday being with others, we are able to tranquilize ourselves and escape the radicalness of the human condition. Angst jerks us out of these pseudo securities. We are made to feel ‘not at home’ in the world, and ‘uncanny.’ Anxiety awakens us from our illusions, and false certainties.”
Kierkegaard= “The nothing that is the object of anxiety becomes more and more a something.”
Heidegger= “Death opens up the question of being..”
Kierkegaard= “terror, perdition, annihilation, dwell next to every man.”
Kierkegaard= “this is an adventure which every human being must go through– to learn to be anxious in order that he may not perish either by never having been in anxiety or by succumbing in anxiety. Whoever has learned to be anxious in the right way has learned the ultimate.”