In Joan Jacobs Brumberg's The Body Project: An Intimate History of American Girls, a book you may have overlooked due to the literally navel-gazing cover, there's a concept I've been thinking about this last week. Brumberg, in her research, read thousands of diaries and magazines and memoirs of teenage Americans from the last two centuries, and, amongst other intriguing discoveries, noticed that although young women have always filled notebooks with resolutions and plans for…