The official line on Back to the Future's origin states that co-writer Bob Gale was visiting his native Missouri, found his father's high school yearbook, and wondered if he'd have befriended him as a teen.
A reader wrote in to ask about this very issue, whether the famed "To Be Continued..." at the end of Back to the Future actually appeared in the original film or if it was added later and people just have convinced themselves that they saw it in the original film.
It's 1985 and the Doc rocks up at our doors offering to take us back in time. You jump into the time machine and suddenly, you come face-to-face with your younger self. What would you tell your younger self?