James teaches that all the following are true causes of unanswered prayers except

James teaches that sin, unfaithfulness, and greed are true causes of unanswered prayers. However, he does not teach that diligence is a cause of unanswered prayers. In fact, James emphasizes the importance of perseverance and endurance in the face of trials and difficulties, and he encourages believers to pray with faith and trust in God's goodness and faithfulness. Thus, James suggests that diligence in prayer is actually a key ingredient in receiving answers to prayer, rather than a cause of unanswered prayers.