Kahlil Gibran - an excerpt from The Prophet

Then a woman said, "Speak to us of Joy and Sorrow."
And he answered:
Your joy is your sorrow unmasked.
And the selfsame well from which your laughter rises was oftentimes filled with your tears.
And how else can it be?
The deeper that sorrow carves into your being, the more joy you can contain.
Is not the cup that hold your wine the very cup that was burned in the potter's oven?
And is not the lute that soothes your spirit, the very wood that was hollowed with knives?
When you are joyous, look deep into your heart and you shall find it is only that which has given you sorrow that is giving you joy.
When you are sorrowful look again in your heart, and you shall see that in truth you are weeping for that which has been your delight.
Some of you say, "Joy is greater than sorrow," and others say, "Nay, sorrow is the greater."
But I say unto you, they are inseparable.