Why are headlines important?

I learned about the purpose of headlines. Headlines are supposed to be short and easy to read, but they also need to summarize the article in a way that a reader gets an idea of the event presented, but also has a hook effect that makes the reader want to know more. An example for the image shown would be "The slap heard 'round the world", because this specific event really had a booming effect in all of media, and it involves a person slapping another.