Imagine you come across two of your friends. There is your dear friend A, talking to your other dear friend B. While they say hi and start talking to you, you suddenly notice their interaction C facing you as solid as your friends are. Somehow you don't like C. There is no animosity in between and their welcome ceremony is warm enough but it's just that you don't like how they effect each other or how their relationship is effecting other people. That C makes you walk away despite your easy friendship with A and similarly easy friendship with B.
Let's take on a more positive example and say you are sort of OK with having A around and you think B is a freak (yes, this is what I call a positive example). Somehow, when they are together, they rock! Being together makes them a fabulous company and the interaction C shines bright. B becomes less of a freak and A becomes more fun to be with. C changes how you perceive their personality eventhough it doesn't in reality. Not that I like Woody Allen but that's the point of the Vicky Christina Barcelona where a couple finds out that the missing part in their relationship is another person. Having mentioned the movie, I have to post its cute soundtrack below.
http://www.youtube.com/watch?v=dEt1H9hkHvE
