In chapters 13, 14 and today鈥檚 reading, Saul begins to act in ways that are more self-assured. He begins to move forward in ways God says are not right and makes rash decisions. As a result, God rejects him as king. The self-assurance that would normally be associated with being kingly is what causes Saul to be rejected.
It鈥檚 odd how Saul鈥檚 humility completely turns around. He was able to handle a little success, but it did not continue. We need to stay vigilant, especially in success. We don鈥檛 want to begin thinking we are no longer in need of God or that we are better than those around us (Romans 12:3).