It's just comparing time and space by analogy. Instead of two related events separated in time, we have the two ends of the popsicle stick separated in space. Obviously if an event A causes an event B to happen, then changing A will have an effect on B. In the same way, pushing on end A of the popsicle stick will affect end B. But with the Popsicle stick things also work the other way around; pushing on end B affects end A too. The jump is made here: if pushing on end B of the popsicle stick affects end A, then couldn't we imagine changing event B to have an effect on event A (even though A occurs before B)?
