It knows where it wants to go and stubbornly resists all attempts to make it go elsewhere. Others have very manageable hair. It willingly does whatever the stylist decides it should do. It knows who's boss and gladly receives all the help it can get. With that help, results can be astounding.
People can be self-willed too.
God knows we need all the help we can get, so He longs for us to give Him control of our lives. Those who yield to God's purposes are not spineless. Having made God's will their own, theirs is the strongest will possible. By exchanging their own agenda for God's, their lives produce some amazing, God-glorifying results. To make something of your life, give your life to God.