Dallas Willard, in The Scandal of the Kingdom:

Humility is one of the main ingredients in prayer because humility shows dependence on God. When we’re not praying, it can be because we have more confidence in ourselves than in God, despite all our failures. We keep thinking, I can handle it; I’ll work it out, rather than crying out, “Lord, help me!” We can get so consumed with trying to prove ourselves and get what we want through our own abilities that we leave no space for God to work with us. We trust only in ourselves.