This quote is so powerful. Sorrow lies in every soul, we all have our silent cross to bear. Your friend must have a tough mindset, to have to cope with a horrible situation and yet to put on a smile at the end of the day.

Light and darkness is the way life works. We can't have only one of them. I think that with time and wisdom we learn to treasure the sorrow and take the lessons out of it, like a precious nectar.