It has been described as a hook for the reader. If you have a poor introduction, you could turn the reader off, and it doesn't matter how good the rest of the essay is. If the reader doesn't get beyond the introduction, your communication is a failure. So, it's worth spending some time on. Although the examples given below are mine, the models are from Canavan and Brandon.
Recent research shows that smokers have a fifty-percent chance of becoming impotent.
If young smokers understood that fact, they might have a whole new idea about what's cool. I'd like to apply for this reporter's job,' he told the editor. It's an unusual way to make a job application, but for Roberto Rodriguez it worked.