The first time I saw a preview for the new movie “Dear John,” I wondered why they would name a supposed love story the term used for break-up letters. All throughout the preview, the main female character, Savannah (Amanda Seyfried), writes letters to her army boyfriend John (Channing Tatum), all beginning “Dear John.” As could be expected, the title—and the use of this line—foreshadow a major plot point.