The idea that close friendships are one of life's great joys should come as news to nobody. Before you and your best friend were friends—and even before you and your best friend were at all—Aristotle mused that, "A true friend is one soul in two bodies." (See? Old news.) But new research suggests that having a best friend throughout childhood can have lasting psychological benefits and improve one's coping abilities in later life. And you thought all you got out of it was that rusty old BFF necklace.