Ben's theory
I have this friend, let's call him Ben; because, well, that's his name. I haven't seen Ben in about 10 years but when I knew him he was married. The woman he was married to was the poster girl for the traditional wife. I'm not sure what that means exactly but Ben was convinced that she demonstrated the qualities that he imagined in an ideal wife. Even though he was married he still managed to appreciate the beauty of women he saw in his day to day life. The people he found attractive were completely different from the person he was married to; nearly diametrically opposite in fact. I asked him about this one day, and he said he believed that, when you're married, the people you find attractive are often very different from the people you're married to; part of what makes them attractive is that they're different. We called this idea 'Ben's Theory'. You might argue that this is somewhat related to the "the grass is always greener" idiom, except that Ben didn't suggest that the married people ever wanted the greener grass, they simply appreciated it because it was different. For a completely different twist on this theory, see Madonna-whore complex.