Introduction to the Art of Singing by Johann Friedrich Agricola

"1. Musical mistakes insinuate themselves so easily into youthful minds and it is often so difficult to find anyone to correct them as they arise, that ideally only the very best singers should undertake the task of teaching, because they, better than any others, know the way to success and, with perceptive insights, are able to guide the student in developing his talent from the beginning stages to perfection."