A long time ago in a galaxy far, far away....
A significant part of any story is exposure, which is how the listener learns about the universe that events take place in. It provides context for events and in the best of cases, compassion for the characters in the story.
Exposure tends to be a difficult thing to do right. Many naive forms of exposure will be forgotten by the listener due to a lack of motivation for them to remember it.
A common way to do good exposure is to mix it with character dialog. That way, the exposure is directly delivered from a character that the listener hopefully cares about. However, this obviously introduces limitations on how much exposure can be told at any one time without breaking the suspension of disbelief.
A bad way to do exposure is to have a long narration in the beginning of the story. There is no better way to have the listener forget everything you just told them.