As he turned away from academic pursuits, Shannon also focused on inviting aspects: It was a game, a problem, a puzzle. It produced motions he considered beautiful. And it was something he simply could not master, making it all the more tantalizing. Shannon would often lament that he had small hands, and thus had great difficulty making the jump from four balls to five — a demarcation, some might argue, between a good juggler and a great juggler. Old friends — fellow jugglers from the Bell Labs days — wrote encouraging letters suggesting he was closer to five balls than he realized. It’s likely Shannon never quite achieved that. Nevertheless, in the late 1970s he found himself consumed by the question of whether he could formulate a scientific theory of juggling to explain its unifying principles. Just as he had done years before — for his papers on cryptography, information, and computer chess — he delved into the history of juggling and took stock of its greatest practitioners.
That is from Jon Gertner’s The Idea Factory: Bell Labs and the Great Age of American Innovation. Here is my previous post on the book, which I recommend highly.