Human life must be some kind of mistake. The truth of this will be sufficiently obvious if we only remember that man is a compound of needs and necessities hard to satisfy; and that even when they are satisfied, all he obtains is a state of painlessness, where nothing remains to him but abandonment to boredom. This is direct proof that existence has no real value in itself; for what is boredom but the feeling of the emptiness of life? If life — the craving for which is the very essence of our being — were possessed of any positive intrinsic value, there would be no such thing as boredom at all: mere existence would satisfy us in itself, and we should want for nothing. But as it is, we take no delight in existence except when we are struggling for something; and then distance and difficulties to be overcome make our goal look as though it would satisfy us — an illusion which vanishes when we reach it; or else when we are occupied with some purely intellectual interest — when in reality we have stepped forth from life to look upon it from the outside, much after the manner of spectators at a play. And even sensual pleasure itself means nothing but a struggle and aspiration, ceasing the moment its aim is attained. Whenever we are not occupied in one of these ways, but cast upon existence itself, its vain and worthless nature is brought home to us; and this is what we mean by boredom. The hankering after what is strange and uncommon — an innate and ineradicable tendency of human nature — shows how glad we are at any interruption of that natural course of affairs which is so very tedious.

Arthur Schopenhauer (1788-1860) German philosopher
“The Vanity of Existence,” Essays of Arthur Schopenhauer: Studies in Pessimism [tr. Saunders (1851)]
    (Source)

Alternate translation:

That human life must be a kind of mistake is sufficiently clear from the fact that man is a compound of needs, which are difficult to satisfy; moreover, if they are satisfied, all he is granted is a state of painlessness, in which he can only give himself up to boredom. This is a precise proof that existence in itself has no value, since boredom is merely the feeling of the emptiness of life. If, for instance, life, the longing for which constitutes our very being, had in itself any positive and real value, boredom could not exist; mere existence in itself would supply us with everything, and therefore satisfy us. But our existence would not be a joyous thing unless we were striving after something; distance and obstacles to be overcome then represent our aim as something that would satisfy us -- an illusion which vanishes when our aim has been attained; or when we are engaged in something that is of a purely intellectual nature, when, in reality, we have retired from the world, so that we may observe it from the outside, like spectators at a theatre. Even sensual pleasure itself is nothing but a continual striving, which ceases directly its aim is attained. As soon as we are not engaged in one of these two ways, but thrown back on existence itself, we are convinced of the emptiness and worthlessness of it; and this it is we call boredom. That innate and ineradicable craving for what is out of the common proves how glad we are to have the natural and tedious course of things interrupted. [tr. Dircks]