It is not always easy to feel thankful. The journey of a human through life is not only joyful, it is also filled with dark times and hard places. Things don't work out, trials are endured, tragedy strikes. We all have those moments where we are overwhelmed by something we must face, and it feels lonely and negative.
It is hard to summon up the gratitude at those times. We wouldn't be human if there weren't resentment, fear, anger, hopelessness, or plain old fashioned unhappiness when things don't go the way we hope.