Love what you do
"That's why he's great; he plays everything as though he's in love with it."
-Niffenegger, page 201
Henry explains to Alicia that music is something that one must be passionate about even when the music is not a particular favorite. He refers to how his father, seccond chair violinist of the Chicago Symphony Orchestra, plays every piece with fervor and dedication, even if he despises the piece. Likewise, Henry feels that Alicia should adopt the same attitude. However, it is sad to see the hypocrisy in the elder DeTamble's ways.
Henry's father has been in mourning ever since the loss of his wife. He has lost the love that is within his heart and soul. Violin playing has become second to drinking, and as we find out later, the drinking destroys his ability to play the violin. Mr. DeTamble loves music...or rather, he loved music, at one point.
It has been 23 years since Mr. DeTamble loved anyone or anything. Henry speaks the truth about musicians' philosophy, but his father mimics his way through the orchestra. His bitterness and self-pity consume him and the music that he had once loved.