Hector Berlioz,
The Orchestral Conductor: Theory of His Art
“ The most formidable, to my thinking, is the conductor of the orchestra. A bad singer can spoil only his own part; while an incapable or malevolent conductor ruins all. Happy indeed may the composer esteem himself when the conductor into whose hands he has fallen is not at once incapable and inimical; for nothing can resist the pernicious influence of this person. The most admirable orchestra is then paralyzed, the most excellent singers are perplexed and rendered dull; there is no longer any vigor or unity ”
