The more you doubt, the more you'll have to live without.
Complaining is one of the worst traps that many Christians fall into. A complainer thinks, "I can't stand my boss. If she would only treat me better, I'd be happy. I hate this traffic. Why can the government improve traffic flow with all the tax money I pay?" This is a deceptive trap because it leads one to believe that life would be better if something would be different. However, it is far more productive for to believe that God can change the situation than to doubt him.
This trap of complaining is the same trap that the Israelites fell into. They were not satisfied with what God had given them and they continually wanted more. Psalm 106:12-15 is a great example of what happens to people who are unthankful and always want more: Then they [Israel] believed his promises and sang his praise. But they soon forgot what he had done and did not wait for his counsel. In the desert they gave in to their craving; in the wasteland they put God to the test. So he gave them what they asked for, but sent a wasting disease upon them.
That passage refers the Israelites' persistent request for food, water, and other basic resources. They didn't trust God; they doubted his ability to provide and tested him. So, because of their doubt, God sent a wasting disease upon them. Furthermore, for forty years God withheld the promised land from them. Their doubt caused them to live without.