I've heard the likely apocryphal story of how the lack of a semicolon in a controller program's source code has led to rocket ships and their passengers falling from the sky to flaming, screaming death.
The lack of a closing quotation mark in a program's source file recently caused the company I work for not to get money from clients who had signed up for things they are supposed to pay for, resulting in most of a day's work on the part of a couple of engineers to rectify everything.
They're not going to fire the programmer who made the mistake for the booboo. It was just one of those embarrassing little things that happen sometimes with software. But the experience illustrates that in software, precision is of the utmost importance.
While I don't wish either flaming death or failure to advance in school on persons who make silly writing mistakes, I do wish in this age of electronic communication that people would take greater care with their written correspondence.
I was working on the proof of one of my poems all the morning, and took out a comma. In the afternoon I put it back again. — Oscar Wilde