" Because around a crisis point, even the tiniest action can assume importance all out of proportion to its size. Consequences multiply and cascade, and anything—a missed telephone call, a match struck during a blackout, a dropped piece of paper, a single moment—can have empire-tottering effects. The Archduke Ferdinand’s chauffeur makes a wrong turn onto Franz-Josef Street and starts a world war. Abraham Lincoln’s bodyguard steps outside for a smoke and destroys a peace. Hitler leaves orders not to be disturbed because he has a migraine and finds out about the D-Day invasion eighteen hours too late. A lieutenant fails to mark a telegram “urgent” and Admiral Kimmel isn’t warned of the impending Japanese attack. “For want of a nail, the shoe was lost. For want of a shoe, the horse was lost. For want of a horse, the rider was lost. "

― Connie Willis , To Say Nothing of the Dog (Oxford Time Travel, #2)