The very transitory nature of life is a cause of suffering, for even happiness is seen to be temporary. While experiencing happiness, which by definition is the absence of pain, one has expectations of the continuation of the state of joy. But these expectations can never be met.
Certainly, this is no rosy-spectacled view of life. Yet Buddhism does not absurdly deny the presence of happiness (sukkha) in human existence. Buddhist texts list various kinds of pleasures, including sensual pleasure and the joy of family life, that one can enjoy, comparable to the list of the common experiences of suffering.9 However, Buddhism does not want us to accept happiness uncritically. Subject to the law of mutation, our feelings and attitudes are liable to change. Similarly, these objects of pleasures (such as a new motor-car, a glass of beer, a girl friend) cannot last long for they contain within themselves the potential for change and decay. Having undergone change and decay, they cease to give us happiness in their new forms. One should always remember that life contains a number of undeniably unpleasant experiences, which nobody could ever pretend are enjoyable, such as old age, disease, death, being separated from what we like, and being associated with what we dislike. All these make up the painful side of existence which humanity tends to ignore.