Throughout its first six seasons, the HBO adaptation of Game of Thrones had a handful of time-travelish moments mostly centered on young Bran’s dreams of the past. But it wasn’t until the origin story of Bran’s half-giant companion, Hodor, that we saw a definitive influence of present-day Bran on Hodor’s past. The interaction is a terrific example of a closed causal loop: Bran is observing Hodor in the past because of who Hodor is to Bran, and it is Bran’s presence that creates that very Hodor.