How we change what others think, feel, believe and do
A tragedy happens when particularly undesirable things happen. In the traditional tragedy this means that major characters die.
A typical storyline has a major character bravely fighting an illness whilst their loved ones look on in despair. 'Tear-jerker' stories like this use copious pathos to trigger emotion.
In the Greek sense, Aristotle defined a tragedy simply as including a reversal or fortunes, including from bad to good. By definition, Greek tragedy included plot (most important for Aristotle), characters, a chorus, thought, diction, music, and spectacle. The meaning evolved from this to anything serious (i.e. not a comedy) to something with an unhappy ending.
William Shakespeare's Romeo and Juliet
Henrik Ibsen's A Doll's House
Arthur Miller's The Crucible
Although it may seem strange to want to experience a sad story, there are several benefits we can get from this. It can provoke our need for stimulation: when you are bored, even sadness is better than nothing.
Seeing others being sad reassures us that we are not the only person who is sad (although sometimes it seems this way as others politely cover up their sadness with a false cheeriness).
Seeing others suffering a deep tragedy puts our petty worries into perspective.
Seeing others handle tragedy can teach us something about how we should handle our own problems.
Tragedies are excellent vehicles for exploring inner conflicts, split personalities, true and false self and other deep psychoanalytic aspects. Values may be explored including the difference between espoused values and values in practice. Tragedies can show how power corrupts and stress can lead to dysfunctional coping.
In his Poetics, Aristotle described tragedy as:
...a process of imitating an action which has serious implications, is complete, and possesses magnitude; by means of language which has been made sensuously attractive, with each of its varieties found separately in the parts; enacted by the persons themselves and not presented through narrative; through a course of pity and fear completing the purification of such emotions.