Funny, how we take for granted that someone is listening when we talk to them. Do you recall ever talking to someone who wasn't paying the slightest attention to you and/or to what you were saying?
The presence of the speaker does make a difference, doesn't it?
A person who dares stand up in front of an audience and address them in song is speaking to everyone in the room.
I remember sitting 4th row center in Alice Tully Hall when Thomas Quasthof sang as his second encore Schubert's An die Musik. It was a Sunday afternoon. My family was in the midst of dealing with unbelievably difficult health issues. Music was saving us, as individuals and as a family. It was inevitable that I heard every sound he made, as if he was addressing me personally. I dissolved in tears. I don't know to this day how he made it through, but after he finished he looked me straight in the eye and said "Thank you."
That is what every singer assumes: We are in this together, never more than right this minute.