When Ness and his friends had to travel to the past to save the world, they used Dr. Andonuts' Phase Distorter. Then thing was, the first prototype required the material known as Xenophyte, which was found in the meteorite that crashed in Onett. Upon obtaining this material, the Phase Distorter sent Ness and his friends to a place in limbo.

Now, when you get there, you can see a crashed machine of some sort. In truth, this actually was another Phase Distorter.

The things is, this leads to a paradox. If Ness originally had crashed and died in the crashed distorter his timeline would have ended - but Dr. Andonuts and Apple Kid had prevented Ness from doing so. So was this a thing needed to do, a loop? Or was it something that had never occured until then?

Another topic that involves this paradox, is when Buzz Buzz explains to Ness about the future. He originally says that 10 years into the future, the world was a dark place and that Buzz Buzz had traveled back through time to change all that.

So when you beat the game, you change the timeline, altering the future to a peaceful one. Thus, Buzz Buzz would have never gone back through time and Ness never battled Gigyas. The question. What is the outcome? Would Ness have continued living his normal life? Or does changing the future, cause an endless loop in which Ness is forever trapped?

This is all to confusing to comprehend. That is why time travel is a tricky thing and has many complications in EarthBound.