Shabbos 75b - A Mistake

We know that there is a melacha of mocheik - erasing. The Rosh explains that this was found in the mishkan when they would accidentally write the wrong letters on a beam and had to cross them out and write them again.

Asked Rav Eliyahu Fischer Shlita, the Gerrer Rosh Kollel: Normally, all melachos in the mishkan were CREATIVE. Even סותר was when they purposefully dismantled in order to rebuild. This whole melacha seems to be built on a mistake.

He answered that writing is fundamentally different than all melachos. Every pencil comes with an eraser [well, most of them]. The reason people like using pencils is so that they can erase. When we write we assume that we will make mistakes. In modern technology it is called "backspace". Writing assumes error and thus the melacha is in fact predicated on error.