I spotted this lovely analogy on the Agile Usability mailing list, from William Pietri, in a conversation about the value of colocating teams:

"Let's consider that archetypal human relationship, romance. We all agree that this works best when collocated. In that context people can establish it without formalism. People do maintain long-distance relationships, but these are usually started in person, they are known to be relatively unsatisfying, they are hard to keep up, and they are more likely to fail. You occasionally hear of people who create real romantic relationships without any collocation, through some interactive medium like letters or telephone calls or email or IM or video chat. With these newer media, I think this has become more common, albeit still rare. And many consider these relationships riskier. It's interesting to note that some people establish imaginary relationships through one-way media. Actors, for example, complain that people on the streets will often treat them as their characters, not as themselves. And the teen in love with a movie star is a classic stereotype."