“The ingredients of both darkness and light are equally present in all of us,… The madness of this planet is largely a result of the human being's difficulty in coming to viruous balance with himself.”

Source: Kierkegaard’s Critique of Reason and Society (1992), p. 49

Source: “What’s wrong with Libertarianism”, p. 427

Also translated as: It is not because things are difficult that we do not dare, but because we do not dare, things are difficult.
Letter CIV, verse 26
Epistulae Morales ad Lucilium (Moral Letters to Lucilius)
Context: But how much more highly do I think of these men! They can do these things, but decline to do them. To whom that ever tried have these tasks proved false? To what man did they not seem easier in the doing? Our lack of confidence is not the result of difficulty. The difficulty comes from our lack of confidence.

Context: And now we are wanting everyone in every country through the education department of every government to unfold that inner content of life. It’s very simple to light the lamp is so easy. And yet that process of lighting the lamp is enough to eliminate the difficulties in the darkness.

XII. The origin of evil things; and that there is no positive evil.
On the Gods and the Cosmos

Source: Pale Blue Dot: A Vision of the Human Future in Space (1994), p. 8, Supplemental image at randi.org http://www.randi.org/images/122801-BlueDot.jpg
Context: Our posturings, our imagined self-importance, the delusion that we have some privileged position in the Universe, are challenged by this point of pale light. Our planet is a lonely speck in the great enveloping cosmic dark. In our obscurity, in all this vastness, there is no hint that help will come from elsewhere to save us from ourselves.
Context: Consider again that dot. That's here. That's home. That's us. On it everyone you love, everyone you know, everyone you ever heard of, every human being who ever was, lived out their lives. The aggregate of our joy and suffering, thousands of confident religions, ideologies, and economic doctrines, every hunter and forager, every hero and coward, every creator and destroyer of civilization, every king and peasant, every young couple in love, every mother and father, hopeful child, inventor and explorer, every teacher of morals, every corrupt politician, every "superstar", every "supreme leader", every saint and sinner in the history of our species lived there — on a mote of dust suspended in a sunbeam.
The Earth is a very small stage in a vast cosmic arena. Think of the rivers of blood spilled by all those generals and emperors so that, in glory and triumph, they could become the momentary masters of a fraction of a dot. Think of the endless cruelties visited by the inhabitants of one corner of this pixel on the scarcely distinguishable inhabitants of some other corner, how frequent their misunderstandings, how eager they are to kill one another, how fervent their hatreds.
Our posturings, our imagined self-importance, the delusion that we have some privileged position in the Universe, are challenged by this point of pale light. Our planet is a lonely speck in the great enveloping cosmic dark. In our obscurity, in all this vastness, there is no hint that help will come from elsewhere to save us from ourselves.
The Earth is the only world known so far to harbor life. There is nowhere else, at least in the near future, to which our species could migrate. Visit, yes. Settle, not yet. Like it or not, for the moment the Earth is where we make our stand.
It has been said that astronomy is a humbling and character-building experience. There is perhaps no better demonstration of the folly of human conceits than this distant image of our tiny world. To me, it underscores our responsibility to deal more kindly with one another, and to preserve and cherish the pale blue dot, the only home we've ever known.

"Beasts Bounding Through Time" (1986)

Variant: ‎"... the sole purpose of human existence is to kindle a light in the darkness of mere being.
Source: Memories, Dreams, Reflections (1963), p. 326

Source: Revolution