Shot/Reverse Shot

Shot/Reverse shot is used when to people are shown talking. When the first person is shown looking to the right, the other person must be shown looking to the left to create the impression for the audience that the two people are looking at/talking to each other. It would be very confusing if both persons were shown looking to the right in their shots, because that creates the impression that they're not looking at each other while talking. 

For example:

Imagine to see a Two-shot like this,

and after that a shot (l.) and reverse shot (r.) like this

or this:

Doesn't really create the impression of the two of them talking to each other.

The right way would be like this: