Taylor is a positive woman who sees living in the world as a manageable challenge. She believes in herself and in others. Taylor has the strength and confidence to strike out on her own, searching for her own life, unencumbered by her family.
Lou Ann, however, is a dependent pessimist. She cares about people, but she is determined to see the worst in life, to read the horoscopes and worry about people. She is more willing to be with an abusive husband than alone. Per Taylor:
"For Lou Ann, life itself was a life-threatening enterprise. Nothing on earth was truly harmless."
Having these two contradictory personalities forces each woman to examine themselves. Taylor, particularly after losing Turtle, begins to see how unfair and unconquerable life can seem to be. She despairs, and begins to take on a bit of "Lou Ann-ness". In turn, Lou Ann is forced to examine her attitude through living with Taylor. She begins to understand that she has been her own worst enemy, and that life will be as good as she makes it.
These internal conflicts allow both characters to grow. Taylor, in the end, is able to remain an optimist, but allows her optimism to be tempered by realism and experience.