Twilight meets Future Twilight, who attempts to warn her not to worry about the future because nothing will happen in the next week. But how did this start? What happened first? It seems that Twilight is doing something because of something that happens in the future, which only happened because of what happened in the past, sparked by what happened in the future. Worse, all of this happens because somewhere along the way, some incarnation of Twilight Sparkle was afraid that her past self would worry about something that didn't happen.
This is the sort of thing that makes people in Star Trek fear going into the past. We are either forced to abandon a linear view of time, or else throw away the whole idea of cause and effect.
Edited by Frankenbrony, 10 May 2012 - 05:17 PM.