"Back to the Future" (the book) and the Butterfly Effect

You all know the geek classic BttF, I guess. (If not, try to fix that gap.) The book is lesser known, although Ryan North (of Dinosaur Comics fame) riffed it in his tumblr blog (yes, these words weren't invented yet when I was born). It has flaws (as he is pointing out), but also contains a great depiction of the Butterfly Effect, on p. 134-36.

You can read it here, but I'll quote Doc Brown here: “That’s a tiny item but it could happen. Let’s suppose the theater operator is looking at the balance sheet one day and thinking about selling. Maybe that extra fifty cents pushed the receipts from $999.75 to $1000.25. That is, it goes from three figures to four figures. That might be the psychological difference between keeping the theater or selling it. So, influenced by the extra fifty cents, he keeps it. Not long afterward, when the theater would be closed if he’d sold it, a fire starts and some people are trapped inside. One of them is a youngster who’s destined to become President of the United States – except that now he’s dead.”

“And I did it,” Marty muttered. “I killed him with my fifty cents.”