The duality of sadness and happiness is the basic cause of suffering. Cessation of suffering, which is nirvana, means going beyond this duality of misery and joy. The Buddha taught the path to freedom from desires, not the way to satisfy them. Mahayana Buddhism teaches that bodhisattvas should transcend even the dichotomy of samsara and nirvana.
Shohaku Okumura, The Zen Teaching of Homelesss Kodo