From the NYT article profiling him for the 50th anniversary of the first publishing of The Art of Computer Programming:
When Knuth chooses to be physically present, however, he is 100-per-cent there in the moment. “It just makes you happy to be around him,” said Jennifer Chayes, a managing director of Microsoft Research. “He’s a maximum in the community. If you had an optimization function that was in some way a combination of warmth and depth, Don would be it.”
Which reminded me of this page on his website I read years ago:
Email is a wonderful thing for people whose role in life is to be on top of things. But not for me; my role is to be on the bottom of things. What I do takes long hours of studying and uninterruptible concentration. I try to learn certain areas of computer science exhaustively
Which itself features a quote from Umberto Eco:
‘I don’t even have an e-mail address. I have reached an age where my main purpose is not to receive messages.’ — Umberto Eco, quoted in the New Yorker