What is Todorov's theory?

— And why should this be used?

Todorov produced a theory which he believed could be applied to any film. He took that all of the films followed a similar narrative pattern that went through the 5 stages of equilibrium, disequilibrium, acknowledgement, solving then equilibrium. These stages are going to be applied to the film theory through it’s own way with slight alterations. Some films don’t end with a closed narrative that returns a re-equilibrium, as they are kept open, it keeps the audience thinking whether the characters are safe and that things have returned to normal. 

5 stages of narrative are shown through:

The beginning - a state of equilibrium - everything is normal so far with no problem with the fictional world.

A disruption - Something that throws the equilibrium off the edge. The problem can be slight and can be built up in a snowball effect to the point of eruption.

The middle - The recognition of the disruption - This is where the audience deals with knowing that a problem has arisen. It is the task of the fictional characters to restore that order.

An attempt to resolve the issue.

The restoration of equilibrium with a closed ending narrative.

A lot of directors do not take this approach because it is too predictable by normal standards and a lot to the community like to watch the unexpected. This was done in multiple films such as Shutter Island and Inception.