Marty McFly: "The almanac. Son of a bitch stole my idea! He must have been listening when I- It's my fault! The whole thing is my fault. If I hadn't bought that damn book, none of this would have ever happened."
Doc: "Well, that's all in the past."
Marty McFly: "You mean the future."
Doc: "Whatever! It demonstrates precisely how time travel can be mis-used, and why the time machine must be destroyed, after we straighten all of this out."