This is a poem I found on the Poetry board on Quora written by a computer science graduate, Rohit Tandon and is one of the very deep insightful treatment on the subject of sorrow I have seen in poetic form in the recent past.
How beautiful moments pass by,
And the sad ones take eternity.
Why the happiness moves away,
Leaving a sorrow of perpetuity.
And the memories come back,
Reminding you of a time that has gone.
And the feelings emerge from the past,
A time that has been left and done.
What slaves are we, of thoughts, of memories,
Of the past that is so weak and yet so potent.
How we wish to be free, and yet be entangled,
Within the chains of our precedent.