I liked his answer for the question - why don’t you do email?
Someone has to not be tweeting all the time, someone has to be thinking about things which need a long attention span and trying to organise material and build up strong foundations instead of rushing off across the frontier. It takes a long time to put out something that has the right style; I have to really think about it and if I’m going to do it right I have to spend a lot of time focussed on it. And I was being treated like an oracle, lots of people from around the world were asking my opinion about whatever, so after 15 years of email I decided that was a life time’s worth.
I can understand why he wants to be on the bottom of things, but I don't get why encouraging people to use postal mail rather than email is supposed to help. Email is just a medium, and it's a much more sensible way to move information around. The widespread habit of checking email every 5 seconds is by no means compulsory. I wonder why Knuth says that the batch mode communication he wants to do cannot be done properly with email.
I think it's just that he's trying to raise the barrier to entry a little higher. If you know you'll get a response in a few days or weeks on paper, instead of a day or two later in your email client, that makes you look for other, quicker ways to get the answer you're looking for, which reduces the load on Knuth (and his secretary).
Someone has to not be tweeting all the time, someone has to be thinking about things which need a long attention span and trying to organise material and build up strong foundations instead of rushing off across the frontier. It takes a long time to put out something that has the right style; I have to really think about it and if I’m going to do it right I have to spend a lot of time focussed on it. And I was being treated like an oracle, lots of people from around the world were asking my opinion about whatever, so after 15 years of email I decided that was a life time’s worth.