When His people complain, God gets angry. Why? I think it's because when I complain I am taking for granted what God has already done for me. I get my eyes on the circumstances I am dealing with and forget that God has given me so much to be grateful for...my health, my wife & kids, my friends & family, etc...
My dad used to say something that truly applies when I'm complaining. He would say..."it could be worse." No matter what I face, things could always be worse.
When I think about it, I really don't have anything to complain about. I'm sorry, God, for the times I have.