“Stubborn as a mule” is a well-known idiom. The Bible actually mentions mules in relation to their stubbornness in Psalm 32:9: “Do not be like the horse or the mule, which have no understanding but must be controlled by bit and bridle.” When it comes to following God’s commands, we should not be stubborn or obstinate or intractable. We must not turn our heads away and “stiffen the neck.” We must learn to yield and be pliable in His hands. It’s not our wish for God to use the bit and bridle on us.