He did not think God could make him the father of many nations when Sarah was old and barren. He did not think God could keep him safe from those who wanted to kill him so they could get at his beautiful wife. So much pain and suffering because his God was small rather than big. Abraham's consecration slackens off because his God is too small. Too many times I have seen the same thing today.
Someone has financial difficulties.
He forgets that God is all-sufficient and more than able to carry him through. So he resorts to shifty methods and tricks of the trade. Or, a man is poor. He forgets that God Almighty is His portion. So he envies the rich and becomes discontented with his condition.