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.

[Daß das menschliche Daseyn eine Art Verirrung seyn müsse, geht zur Genüge aus der einfachen Bemerkung hervor, daß der Mensch ein Konkrement von Bedürfnissen ist, deren schwer zu erlangende Befriedigung ihm doch nichts gewährt, als einen schmerzlosen Zustand, in welchem er nur noch der Langenweile Preis gegeben ist, welche dann geradezu beweist, daß das Daseyn an sich selbst keinen Werth hat: denn sie ist eben nur die Empfindung der Leerheit desselben. Wenn nämlich das Leben, in dem Verlangen nach welchem unser Wesen und Daseyn besteht, einen positiven Werth und realen Gehalt in sich selbst hätte; so könnte es gar keine Langeweile geben: sondern das bloße Daseyn, an sich selbst, müßte uns erfüllen und befriedigen. Nun aber werden wir unsers Daseyns nicht anders froh, als entweder im Streben, wo die Ferne und die Hindernisse das Ziel als befriedigend uns vorspiegeln, welche Illusion nach der Erreichung verschwindet; oder aber in einer rein intellektuellen Beschäftigung, in welcher wir jedoch eigentlich aus dem Leben heraustreten, um es von außen zu betrachten, gleich Zuschauern in den Logen. Sogar der Sinnengenuß selbst besteht in einem fortwährenden Streben und hört auf, sobald sein Ziel erreicht ist. So oft wir nun nicht in einem jener beiden Fälle begriffen, sondern auf das Daseyn selbst zurückgewiesen sind, werden wir von der Gehaltlosigkeit und Nichtigkeit desselben überführt, und Das ist die Langeweile. Sogar das uns inwohnende und unvertilgbare, begierige Haschen nach dem Wunderbaren zeigt an, wie gern wir die so langweilige, natürliche Ordnung des Verlaufs der Dinge unterbrochen sähen.]

Arthur Schopenhauer (1788-1860) German philosopher

Parerga and Paralipomena, Vol. 2, ch. 11 “The Vanity of Existence [Der Nichtigkeit des Daseins],” § 146 (1851)
    (Source)

(Source (German)). 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]

That human existence must be some kind of error, is sufficiently clear from the simple observation that man is a concretion of needs and wants. Their satisfaction is hard to attain and yet affords him nothing but a painless state in which he is still abandoned to boredom. This, then, is a positive proof that, in itself, existence has no value; for boredom is just that feeling of its emptiness. Thus if life, in the craving for which our very essence and existence consist, had a positive value and in itself a real intrinsic worth, there could not possibly be any boredom. On the contrary, mere existence in itself would necessarily fill our hearts and satisfy us. Now we take no delight in our existence except in striving for something when the distance and obstacles make us think that the goal will be satisfactory, an illusion that vanishes when it is reached; or else in a purely intellectual occupation where we really step out of life in order to contemplate it from without, like spectators in the boxes. Even sensual pleasure itself consists in a constant striving and ceases as soon as its goal is attained. Now whenever we are not striving for something or are not intellectually occupied, but are thrown back on existence itself, its worthlessness and vanity are brought home to us; and this is what is meant by boredom. Even our inherent and ineradicable tendency to run after what is strange and extraordinary shows how glad we are to see an interruption in the natural course of things which is so tedious.
[tr. Payne (1974)]