Not up to form, because …

Harvey Sach’s comments on pianist Author Rubinstein at age 13:

…it is clear that Arthur’s practising began to deteriorate when he was about fourteen years old.  He would mechanically play through one-handed exercises and use his free hand to feed himself chocolates or cherries, while he read a book that he had propped up on the music stand.  “The result was disastrous, of course, and I was always having to make feverish last-minute preparations for my lessons” [Rubinstein recalls].

 Coincidentally, Rubinstein was very preoccupied with love interests at this time.

 Source: Sachs, Harvey (1995) Arthur Rubinstein.  London: Phoenix, p. 43.