Socrates never wrote anything down, but Plato did, so ironically now we know about Socrates' disdain of writing through Plato's writings (in this case, the Phaedrus). Quoting a paraphrase from Wikipedia [1]
"... writing can do little but remind those who already know. Unlike dialectic and rhetoric, writing cannot be tailored to specific situations or students; the writer does not have the luxury of examining his reader's soul in order to determine the proper way to persuade. When attacked it cannot defend itself, and is unable to answer questions or refute criticism."
[1] https://en.wikipedia.org/wiki/Phaedrus_(dialogue)#Rhetoric,_...
