Sadness is an emotional pain associated with, or characterized by, feelings of disadvantage, loss, despair, grief, helplessness, disappointment and sorrow. An individual experiencing sadness may become quiet or lethargic, and withdraw themselves from others. An example of severe sadness is depression, a mood which can be brought on by major depressive disorder or persistent depressive disorder. Crying can be an indication of sadness.

Sadness is one of the six basic emotions described by Paul Ekman, along with happiness, anger, surprise, fear, and disgust.: 271–4 

Source: Wikipedia

Despite a greatly increased standard of living, people in the USA reporting that they were "very happy" were no more numerous in 1991 than in 1957. Professions with the highest proportion of unhappy people were doctors and lawyers (who are also in the highest income groups in the USA).
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(F) Fuzzy exceptional problems