My Lectio reading for today (actually from the One-Minute Bible for Students) opens with Psalm 104: 31-34:
May the glory of the Lord last forever
The Lord rejoices in all he has made!
The earth trebles at his glance;
the mountains burst forth into flame at his touch.
I will isng to the Lord as long as I live.
I will praise my God to my last breath!
May he be please by all these thoughts about him,
for I rejoice in the Lord.

The commentary talks about the difference between happiness and joy. It says that happiness is dependent on circumstances but that joy is a continuing attitude that doesn't change when situations change. I find it interesting to apply this to God. Psalms says that the Lord rejoices in all he has made--a continuing joy that doesn't disappear no matter how much we mess things up or disappoint him. I think that explains a lot.