A few favorites...
(These and others - to be revised)
Sibelius met Mahler in Helsinki in 1907. They compared notes and found that with each new symphony they had lost listeners who had been captivated by the previous symphony. They disagreed about the symphony as a musical form. Sibelius: “I said that I admired its strictness and style and deep logic, which requires that all its motifs must be linked to each other.” Mahler: “No, the symphony must be like the world. It must encompass everything.”