If I am thankful for the good in my life, the good truly benefits me. I have the joy of it. I embrace it to myself and it defines me. The more I am thankful for, the more I see to be thankful for, and my joy and contentment grow, even in the presence of sorrow and difficulty.
If I don't take note of the good with thankfulness, I stand away from that good. It should be mine, but I don't really have it. I am defined instead by the lack which is all I am taking note of. I don't receive the good until I step toward it with open arms of gratitude.
Without thankfulness, I starve in the midst of plenty, because I am not partaking of the feast God is always setting.
We can never know how rich we are until we say thank you.