Steppenwolf by Hermann Hesse (1927)

Somewhere on a wall in a grey northern city a sign flickers into being: Magic Theatre, for madmen only, and the price is your mind. Harry Haller, a greying intellectual lodging in a tidy bourgeois house he both reveres and can't stop sneering at, has spent years certain he is two creatures sharing one skin: the man who weeps at Mozart and the wolf of the steppes who would tear the whole comfortable world to pieces. Hesse lets that diagnosis stand just long enough to take it away. Hermine, a dancer who refuses to treat his despair as sacred, teaches him to waltz, to laugh, to suspect his sharpest self is not his only one. The book's quiet, devastating claim is that no one is two natures; everyone is a thousand, and to call yourself a single type is to lock the rest of yourself in a cell you furnished. Read it the next time you have decided which animal you are.