All sentient beings naturally desire happiness and comfort because our true nature of mind Buddha Nature is of total peace happiness love and is undefiled. So we desire these qualities externally to be in line with our inner true nature. Our true nature of mind is temporarily clouded by adventitious defilements like clouds blocking the sun rays. Still the clouds cannot totally obscure the sun (our true nature of mind). Thus when we suffer we desire peace and happiness. We need to know that self-grasping is the root cause of all suffering (since the notion of self does not exist in our inner true nature of mind) whereas altruistic mind (which is our inner true nature of mind) is the root cause of all happiness.
