It is just as important to remember this on the really great days as it is on the rough days.  To be IN this world, but not OF it is a walk of faith and a mindset which determines to trust God despite our feelings toward our current circumstance...to respond to everything with love....to know we belong to God and to be longing to be with Him.  You can be a Christian and find yourself in places where you are focused on your circumstance and not on the One who will carry you through it.  God has used a few hardships in my life to remind me of this truth and to train me to be grateful for the things He gives and the things He takes away because no matter how I feel about them, they are His perfect plan for me.