One day, as we were reading an email to our advice column Direct Answers, Tamara looked up and said simply, "She doesn't know what a friend is." That line-she doesn't know what a friend is-has come back to us again and again as we read letters about a problem with a friend. Although we didn't realize it at the time, that is how The Friendship Solution began. We wrote this book for two reasons. First, when many people use the word "friend," they are actually describing a frenemy, a person they dislike, a rival or an antagonist, or a person who manipulates them. They are not talking about a true friend, someone they know and like, someone they can trust to have their back. Understanding this distinction is one of the keys to having a good life. But understanding this distinction is not enough. We must act on it. That is the second purpose of this book. We want to explain why we need to sort people out based on where they should fit in our life. Some dictionaries define a friend as someone we know well and like, exclusive of sexual or family ties. In this regard, dictionaries are behind the times. More and more, psychologists are seeing our friends, family, and romantic relationships not as fundamentally different but as tributaries of the same river. That is why when we speak of friends in this book, we include traditional friends as well as relatives and romantic partners. The Friendship Solution is about the place of friendship in all our relationships. It is about why we have friends, what a good friend is, learning to say no, and letting go of bad friends. Through letters and research, we will paint a portrait of friendship as it is and as it should be. Finally, this book is a long answer to a short letter, a letter we got on the day Tamara looked up from an email and said, "She doesn't know what a friend is."