I think Sleepless In Seattle is the greatest testament to it. I mean, all it takes is that one scene where he sees her at the airport. And they only interact once, very briefly [i.e., their "hello"s in the street], before the hand-holding ending. But it's believable, with them -- their chemistry sells it.
Back on topic, though. The best You've Got Mail quotes from Kathleen [Meg Ryan]:
"The odd thing about this form of communication is that you're more likely to talk about nothing than something. But I just want to say that all this nothing has meant more to me than so many somethings."
"Soon it will be something really depressing. Like a Baby Gap."
"It happened in Spain. People do really stupid things in foreign countries."
"You poor, sad, multimillionaire. I feel so sorry for you."
"All that means is that it wasn't personal to you. But it was personal to me. It's personal to a lot of people. And what's so wrong with being personal, anyway? Whatever else anything is, it ought to begin by being personal."
"But the truth is...I'm heartbroken. I feel as though a part of me has died and my mother has died all over again and nothing will ever make it right."
"Sometimes I wonder about my life. I lead a small life. Well, not small, but valuable. And sometimes I wonder, do I do it because I like it, or because I haven't been brave?"
"But there's the dream of 'someone else'."
And, one of my favorite exchanges ...
Kathleen: Why did you stop by again?
Joe: I wanted to be your friend.
Kathleen: Oh.