There is a huge difference in my opinion between optimism and faith.
Optimism is all about always seeing the glass half full, and always seeing the good part of every situation. The problem is, life can really suck sometimes, and it does no good to half a false optimism about how everything will be perfect in the near future when you know things will never be the same again.
Faith is about trusting God that I will be taken care of someway and somehow and that everything will work out for the best. I can have faith, even when I feel down and pessimistic about things. Things may never be the same, and may never be as good as I once had it, but I can have faith that God will be with me through the good times and the bad.
Obviously this theory needs more thought in order to be articulate about it, but that is the theory for today.