by pieces of moments
You must try to discover how high your tolerance is for the is for the questions you ask of yourself. You must try to recognize that point beyond which the creative exploration – questions that extend your vision of your world – extends beyond the point of tolerance and paralyzes the imagination by confronting it with too much possibility, too much speculative opportunity. To keep the practical issues of systematized thought and the speculative opportunities of the creative instinct in balance will be the most difficult and most important undertaking of your lives in music.
From a graduation speech delivered in November 1964 at the Royal Conservatory of Music at the University of Toronto, reprinted here.