To err is human. But some are more human than others. Especially scribes. Writing in the age of scribes and copyists saw the proliferation of textual errors. Nowadays, we are used to introducing mistakes into a text only at the authorial and editorial stage. The printer doesn’t err, it simply reproduces the errors which have already been entered.
The scribes, on the other hand, were experts of error. It is astonishing that the reproduction of written culture was still able to reduce the rate of error to levels which didn’t impact the substantial quality of the texts involved. Imagine broadcasting an image which multiplies the noise geometrically each time it is emitted. What you end up with is a different image altogether, 100% noise which makes the original picture completely unintelligible. But the scribal culture developed means of reducing the noise. The scribes multiplied the errors through the simple act of manual copying, but they also helped reduce them through correction and revision. Not every text copied before the Gutenberg printing press was corrected and revised, and we may estimate that only one in a hundred manuscripts underwent serious correction. But this was nevertheless enough to keep the errors level within acceptable limits so that the written culture of the ancient Mediterranean could survive, when it did survive, in textually reliable form, into the 15th century. Scholars are still struggling to correct some errors due to layers upon layers of scribal oversights – layers so thick that they tended to become normative, leading to significant semantic shifts.
So we may say that the scribes had the poison but also the cure of the reproduction of textual culture. The villains and heroes of the same piece.