For those of us who need to do research to get this joke, I already did it. They mean Rubicon River (which is no longer in the north, so don't look for it there, it's on the opposite side of the knee).
For more context, the Rubicon is famous less among geographers and more among historians. Famously, the governor of a province was not allowed to bring an army south of the Rubicon into Italy, so when Julius Caesar marched south with his army, that is the point at which it was impossible for Rome not to go to civil war. The phrase "crossing the Rubicon" is an English-language idiom (I don't know if equivalents exist in other languages, though I wouldn't be surprised if it's common across countries formerly in the Roman Empire) meaning "passing a point of no return".
I always thought writing essays was the stupidest part of any class because it's entirely up to the teacher's viewpoint on whether the essay was good or not. I finally had a prof in college that REQUIRED us to have a meeting with him with our first draft in hand so that he could critique them before actually turning them in for grading, and suddenly it became so much easier to get good grades on essays.
...yes it literally does lol. Pressing save doesn't magically create a check point or something. You literally said you write it all out then go back. It doesn't matter if you do this in one sitting.