Sri Aurobindo
Letters of Sri Aurobindo
Volume IV - Part 3
All that [sense of grief and sorrow] is probably things that rise 
from the subconscient – or perhaps the subconscient itself is being worked upon to arrive at a state of light and peace. It sometimes enters into a happy condition, sometimes into a neutral one, sometimes it raises up a causeless sorrow. The movements of the subconscient take place even without reason, of themselves, owing to the inherent habit in Nature, that is why the grief is without discoverable cause. It is only because it is in the subconscient that you cannot locate it. When the grief comes, you must dissociate yourself from it and reject it, not taking it as your own, until it ceases to come and call down the Mother’s peace and Ananda in its place.