A lot of speakers have been trained to maintain eye contact with an audience by looking around an audience, that is left front, left rear, right rear then right front. Often they never really look anyone in the eye or make a personal contact. I have learned that if I really get intense with one person that through the process of empathy, everyone in the audience sits in the chair of that person I am focusing on.
The same force works when you single someone out for criticism or poke an ugly joke at someone. The whole audience sits in the seat of that person you embarrass.
Really talk to somebody in the audience, then really talk to somebody else. You can do a one on one with several thousand people through the power of empathy.