The idea of catharsis is a very old one indeed. It was first put into words by the ancient Greeks, referring to the feeling that should sweep over an audience at the ending climax of a tragedy. The basic premise is that the audience will feel relief that there are people, even fictional people, who must deal with far worse things than they themselves.
Catharsis is also closely related to the idea of schadenfreude, which is taking pleasure in the misery of other people. The difference is really an academic one in some circumstances though. Whether you’re taking pleasure in watching a video of a guy getting kicked in the nuts and laughing at his misfortune, or laughing with relief that at least that isn’t happening to you makes no difference. The act is still causing laughter.
However, catharsis is more widespread than schadenfreude. Catharsis is generally any emotional cleansing that happens when you see someone who is dealing with things that you are not. This is the reason that lots of literature is so enduring. For instance, reading a story by Charles Dickens about people who have to slave and toil in the miseries of London can cause great catharsis in the reader. Seeing the misery and filth that infuses a story can relieve a reader’s worries, at least temporarily, about their own past due bills and rent money.
It likely wouldn’t be too much of an overstatement to say that it’s the cathartic potential of literature that keeps many people reading books. If a person isn’t feeling good, which could be anything from sadness to stress, losing themselves in a highly emotional tale can be very therapeutic. Seeing the stress that characters have to go through, and knowing that it’s endlessly worse than what the reader is currently going through, can put things in perspective.
Of course, there’s the additional fact that fantasy and a break for the mind may be just as important as any actual catharsis that occurs because of literature. Literature, and fiction in general, are such enduring forms of entertainment because of the emotional effect on the reader. Sometimes the reader is enthralled by a story because they want to see how much worse the plight of a character can become. Then they can take cathartic comfort from knowing that, as bad as things are in the real world, they aren’t that bad.
There are other times though that the reader doesn’t want to see how bad things can get for the characters in fiction. Sometimes readers simply want to lose themselves in a fantasy world, and to allow themselves, if even for a short time, to become a part of something different than their regular life. They want to run through the streets of London with Sherlock Holmes, shiver in terror with Henry Jekyll, or pull a trigger in a former Eastern Bloc country with James Bond. This fantasy though may be the form that catharsis takes – allowing the reader to forget their own troubles so that when they return to themselves, their own troubles seem much easier to deal with than before.