Let us see just how deep the rabbit hole goes….
When Aaron(2) arrives at his home, he looks in and sees Abe, Kara, and himself talking about time travel. Should he break in that evening and drug the milk? (Does Filby drink milk too?) Let us say that in the last timeline, Aaron(2) fail-safed because Aaron(1) was not drugged, which led to him causing serious complications. As Aaron(2) thinks about the timeline he is in, is it a rewrite of the last timeline or is it a new timeline that his travel has created? First, he must consider if in the previous timeline, was Aaron(1) really Aaron(1)? Was it Aaron(3) pretending to be Aaron(1)? Second, is he really looking at Aaron(1) now? Has Aaron(3) arrived already and taken Aaron(1)’s place? Is Aaron(3) merely repeating the conversation as Aaron(2) remembers saying it when he was the original Aaron? There is no way for Aaron(2) to know. (He might check the attic later.) Third and most importantly, the timeline that Aaron(2) remembers as the last one he experienced may not be the real previous one. It is completely reasonable to conclude that Abe(2) or Aaron(3) used the fail-safe in the last timeline. Since this action affected Aaron(2)’s memory, he does not have any recollection of those events. He will only remember the last timeline that he exited from! The same is true for any other time traveler in the Primer universe.
The whole scene may seem to be a classic comic chase scene; chasing and being chased by one another, running around, and creating havoc, until one of the characters jumps into the fail-safe and restarts all of the events. This factor of the plot is what makes it so difficult to begin or conclude any discussion about Primer. It is what makes the bench scene mind-numbing when examined in detail. The end of the film is also special. The end is a new beginning.
