I would have define tragedy by when a story takes a the main character and the story ends in a poorly for the character. The tragedy is out of the characters control and could not change his fate that happens to him. I think tragic story like to prey on a lot of humans fears and emotions. Aristotle defines it such that it a reversal of fortune. It can be both bad to good and vice versus. But it better when it good to bad because it preys on the audience fears and pity. It helps clear the audiences emotions according to Aristotle and the tragedy is caused by the heroes actions and it had a negative impact in a way that was unforeseen.