We humans living in this world of duality must face sadness, if we know joy, for one always follows the other, joy to sadness, sadness to joy. Some gurus will tell us to rise above emotions, feel neither joy nor sadness, only equanimity. I prefer to embrace them both and learn to manage the energies.
The root of joy is Love, that powerfully expansive energy that opens our hearts and connects us to all that is; and the root of sadness is fear, that constrictive energy that prevents us from embracing the unknown (e.g. what happens when we die) as well as the known (e.g. that after someone dies, we must go on without them). In order to strike a balance between these two opposing energies we must train the mind never to run from sadness, dwell on it, or see it as the enemy, and we do this first of all, by:
1) reminding ourselves that we are forever safe in the Light of the Divine. Then we must accept that,
2) it is what it is: a learning tool, just like joy – both tools designed to keep us centred. Joy reminds us of why we came to earth in the first place and just in case we become too attached to this dimension, sadness reminds us that this is not our permanent home and that we must one day leave to return to the Light from whence we came.