Tolstoy's Anna Karenina opens with the following line
"Happy families are all alike; every unhappy family is unhappy in its own way."

This has stuck with me since the day I read the book. Isn't happiness just one emotion and sorrow a myriad ? Happiness lacks the depth of sorrow. Sorrow makes us who we are by teaching us lessons that Joy is ignorant of. Makes us question and makes us believe. We emerge stronger and humbler from each sorrow and joy often just makes us arrogant and complacent. In sorrow we appreciate everything that was and that could have been and learn to treasure what is. And therein springs the joy and desire for life and living.

says the Prophet (gibran) of Joy and Sorrow

"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? "

I have always thought that crying is cathartic. Its raining outside.