Communication is in fact one of the most basic human functions.
The reason is people. People like you and your audience. We all realize an audience's opinion of a speaker can be formed even before the introduction is complete. The window for audience connection can remain open, or close quickly, depending on your ability to make a strong first impression. But even after you make a successful first impression, your presentation's content can cause those same heads to nod in agreement or to shake in confusion or outright disagreement.