Our Scripture reading today is 1 Corinthians 10:30-31.
Verse 30, "For if I by grace be a partaker, why am I evil spoken of for that for which I give thanks?"
Every child of God has been a partaker of His grace over and over again.  His grace was freely given to us for salvation as well as for our daily Christian walk.  Romans 3:24, "Being justified freely by his grace through the redemption that is in Christ Jesus:"  1 Corinthians 2:12, "Now we have received, not the spirit of the world, but the spirit which is of God; that we might know the things that are freely given to us of God."  God gives freely because God is love.  
Part of God's revealed will is that we give thanks in everything.  1 Thessalonians 5:18, "In every thing give thanks: for this is the will of God in Christ Jesus concerning you."  Christians that desire to be in the will of God and stay in the will of God, must be thankful.  Yes, there are many disappointments that come our way that could cause us to be bitter at God.  In some way, even the low moments of life are for our good and His glory.  We are to give thanks now and we will understand it better by and by.