When relationships start, enthusiasm for our partners is typically natural and intense. We think of them constantly, we want only to spend more time in their company, we delight in their many skills and accomplishments: but this early phase of powerful admiration and longing rarely lasts. The world often explains this cooling as an inevitable result of sheer exposure. It is, they say, typical to neglect what is always around. But the true reasons seem more complicated, more psychologically rich and, in their own way, a lot more hopeful.