I came across this quote while wrapping up Style: Toward Clarity and Grace, one of my favorite books on the craft of writing. The quote is remarkable not only for its content, which is spot on, but its.. clarity and grace:

The secret of the enjoyment of pleasure is to know when to stop … We do this every time we listen to music. We do not seize hold of a particular chord or phrase and shout at the orchestra to go on playing it for the rest of the evening; on the contrary. However much we may like that particular moment of music, we know that its perpetuation would interrupt and kill the movement of the melody. We understand that the beauty of a symphony is less in these musical moment than in the whole movement from beginning to end. If the symphony tried to go on for too long, if at a certain point the composer exhausts his creative abilities and tries to carry on just for the sake of filling in the required space of time, then we begin to fidget in our chairs, feeling that he has denied the natural rhythm, has broken the smooth curve from birth to death, and that though a pretense of a life is being made, it is in fact a living death.

Alan Watts, The Meaning of Happiness.