Primer: Happened What?

Confused by the title? You should be. The title of this post, like the movie Primer, highlights the confusion produced by a non-linear timestream. What I understood of primer was only a basic gist of the plot, but that was definitely intended by the writers. Essentially, two young men invent a device that allows them to travel back in time, and abuse it to rewrite history, becoming rich and using the device to prevent a shooting. It all goes awry when the paradoxes kill a family friend who accidentally discovered the machine. Time blurs as the two go back in time once more to undo the paradoxes, and ensure that events progress as they did originally. This is an issue of time travel, because while to those engaging in time travel, events still progress linearly, to an observer, the end may come before the middle, and the beginning may be rewritten. It is all highly confusing, and not only do paradoxes pile up,  but the human mind begins to lose track of all the changes and variations in the timestream. The mind is built to handle a linear progression of cause and effect, Primer deals with what happens when that order is scrambled.