He had a point on both counts. For example, when I began to think about this topic my recollection was that it was Thoth, not Thamus, who disparaged writing - but a quick internet check soon corrected my bad memory. If I'd been writing in the pre-internet age, I'd have looked it up in my copy of the Collected Dialogues, which I can see from where I'm sitting. Either way, if I'd then chosen to write a post like this one it would have looked as if I'd known it all along, which would I suppose would have been deception of a sort. On the other hand, isn't it better that I'm not spreading misinformation?
Probably Thamus was too negative, looking at only one side of the equation and ignoring the extent to which knowledge is a communal possession and a community enterprise. Still, haven't I avoided getting satnav for precisely his reasons? And I didn't I feel justified in that stance the other day, when I was told of a woman who had visited the house in the Gower four times before letting drop a remark that revealed she believed herself to be in North Wales? Driving from England, she had blindly followed the satnav's instructions, and knew no better. I can hear Thamus scoffing now.
Digression: I assume that in illiterate societies mistakes do occur in the transmission of stories and learning, even well-trained memories being fallible. I wonder if they happen in universal and systematic ways, so that they can in principle be reverse-engineered from the ways that stories are told at later dates - rather as philologists are able to work out the form of long-dead languages by studying extant ones? Are there people who do that kind of thing, combining cognitive psychology and narratology? Palaeosemiologists, shall we call them? I assume Jacob Grimm had something of the kind in mind when he turned his mind to studying Teutonic mythology, but what became of that fledgeling science thereafter?