Then again, how insatiable a creature is man! Every satisfaction he attains lays the seeds of some new desire, so that there is no end to the wishes of each individual will. And why is this? The real reason is simply that, taken in itself, Will is the lord of all worlds: everything belongs to it, and therefore no one single thing can ever give it satisfaction, but only the whole, which is endless. For all that, it must rouse our sympathy to think how very little the Will, this lord of the world, really gets when it takes the form of an individual; usually only just enough to keep the body together. This is why man is so very miserable.
Arthur Schopenhauer, THE VANITY OF EXISTENCE, The Essays of Arthur Schopenhauer; Studies in Pessimism