Arthur Schopenhauer
Publisher: Dover Publications (2006)

The whole foundation on which our existence rests is the present - the ever-fleeting present.  It lies, then, in the very nature of our existence to take the form of constant motion, and to offer no possibility of our ever attaining the rest for which we are always striving.  We are like a man running downhill, who cannot keep on his legs unless he runs on, and will inevitably fall if he stops; or, again, like a pole balanced on the tip of one's finger; or like a planet, which would fall into the sun the moment it ceased to hurry forward on its way.  Unrest is the mark of existence.