Kierkegaard wrote about the absurd, all the while defending religious faith. He called acceptance of the absurd "demoniac madness," and said that a person who refuses to accept unfounded beliefs "rages most of all at the thought that eternity might get it into its head to take his misery from him!"
Kierkegaard defends the "leap of faith," the acceptance of something that is not necessarily true. He admits that there can be no rational purpose to life; even if life's purpose is determined by god, what is the purpose of god? So the absurdity of human existence is not in anyway assuaged by the concept of god, because god's existence is equally absurd, if not more so.
I, as a human being, am doomed to die. Likely, this will be the end of my awareness, something to which I feel a strangely powerful attachment. So, I experience fear, though I know nothing of what it will be like to die, and can hardly expect that existence following death will be in any way unpleasant... or in any way anything!
Yet, as a "sane" person, I go about my daily life, working, resting, talking, engaging in a repetitive life that seems as if it's always been, and will always be.
This is absurd. Would I really be doing the dishes if the shear, animal terror of death were truly in my mind? Looming at the end of my short life, with the seconds flying by and completely out of my control, lies my end. My decease. The black pit that I hurtle toward every moment.
All that I do to "improve" myself will be gone in that instant. All that I am will be forgotten not long after. This flourishing planet, covered in life, is just in a transient state, but will eventually reach the steady-state: lifeless, cold, silence.
And we take ourselves so seriously! It's hilarious, really. We think we matter. We think that anything matters!
And when we can't ignore death, we turn to the wild realm of fantasy. Religion, superstition, spiritualism, pantheism... all coping mechanisms evolved by a bunch of primates who have been the victims of runaway brain evolution. We are too smart, and so our nature is to cling to denial.
What separates man from the animal? Not a whole lot, genetically. Tool use, abstraction, language... these can all be found in the animal kingdom. But no other species does much of what we do... why?
Maybe it's because no other species has stumbled upon the ability to clearly and systematically describe their own existence. Human beings are the one species that we know can gaze into the abyss and realize that all we have, all we are, and all we do is for naught.
In response, we become nature's masters of self-distraction. We fight, we pray, we pretend the dead are still around somewhere. We build, we make up words like "destiny," and we try to force a place for ourselves on the uncaring universe.
As someone willing to distract myself by undertaking pursuits that will allow me to further distract myself in the future, I am called "sane" or "well-adjusted."
And when a person talks about the absurdity of life and existence, others dismiss her. They smile knowingly, having perhaps experienced a tiny hint of existential crisis in the past. But they are beyond such things. They have managed to not believe in death.
The ultimate human triumph is denial, for without it, the human race might see themselves clearly.