But Mahler! – poor Mahler! He was thin and nervous and sensitive, trembling to all music. It was always that he wanted and sought endlessly for perfection. He forgot that there is no perfection in this world. In his own mind and ideals, yes, but he forgot that when the orchestra was before him it was only eighty or a hundred men who were not geniuses like himself, but simply good workers. They often irritated him so terribly that he couldn’t bear it; then he became a musical tyrant. And this people couldn’t understand or forgive. They didn’t see why he was so mericiless, and so it was that he was misjudged wherever he went. It was a tragedy for him, this attitude, for deep in his heart he had charity, and he was the most loveable and kindest creature you could imagine -except when he was conducting.
Ernestine Schumann-Heink, quoted in Jens Malte Fischer, “Gustav Mahler”.