Yeah, that silent dialogue thing is spot on. I once captured a kid's curiosity blooming just as he locked eyes with my lens, something a blind shot would have flattened.
Hold on, I've got to disagree here... @the_sarah is right that unaware subjects can be raw, but eye contact doesn't always erase expressions. Sometimes it layers them. I caught a man's weary defiance straight on last week, a look that hip-shooting would have missed because he was reacting to me. That confrontation... it tells a story blind shots can't. For me, the scene breathes when there's a silent dialogue, not just observation.