Just as an art student knows that negative space around an object is what creates the outline of positive space in a drawing, the enlightened Taoist knows that suffering, pain and misery are necessary for traits like contentment, pleasure, and happiness to exist. Sickness and health are the same phenomenon; they are just at far ends of that same phenomenological spectrum. Masculinity and femininity are also the same thing; they are both the phenomenon of gender expressed in opposite ways. Love and hatred are also the same phenomenon, and so on.