"O give thanks unto the LORD; for he is good: for his mercy endureth for ever."
I'm afraid Christians oftentimes are forgetful to give thanks to God for all that He has done. God's goodness and mercy is exhibited to us in so many ways that we frequently forget to thank Him. Most of the time, our thankfulness to God is a "by-the-way" moment. Instead of immediately showing our gratitude to God, after basking in the moment of His goodness and mercy we remember to thank Him when thankfulness should have been our first reaction. We have to be careful that we don't become so accustomed to God's goodness and mercy that thankfulness is only a "by-the-way" moment.