The cause of all our pain and suffering is not knowing that life and death are illusions; or to put it another way, not knowing that the bardos of life and death are mere projections. As we imagine that everything we see and experience truly exists, we misinterpret our perceptions and then we suffer. When we chant om mani padme hum we purify those misperceptions.

-- Dzongsar Khyentse Jamyang Rinpoche