On Creativity:
From Nicolai Malko's book "A Certain Art". A quote which he attributed to his theory teacher at the St. Petersburg Conservatory, Anatol Liadov:

[in the context of a theory class]

      "What is this?" he [Liadov] would say with a wry face looking through an exercise
      "I wanted it to be different," might come the answers.
      "Different? Oh, yes, I am tired of going through the door. I will climb through the window. Tired of putting shoes on my feet, I will put them on my hands." He would look further. "And what is this?"
      "I wanted to use both rules here, Anatol Konstantinovitch."
      "Oh yes, tea with milk and lemon at the same time . . ." All of this spoken in a monotonous half voice.
       But this manner was not due to indifference. Liadov was an alive, refined and sensitive musician. It seemed that his manners and behavior were reflecting an inner modesty and reserve. This was the secret of his charm. His attitude toward the composer was demanding and strict. "If I have a lucky idea," he would say, "but am not able to use it according to form and logical justification, I should give it up."
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On Thoroughness:
From Herbert L. Clarke's book "How I became a cornetist" published by Leblanc, Inc.

THE IMPORTANCE OF THOROUGHNESS:
It was this strictness of musical atmosphere which was the foundation of my success later on. I never was permitted to let the slightest mistakes pass uncorrected when practicing but was taught to correct and conquer even the most simple one immediately; while still but a child, I was instructed in carefulness; carefulness in holding the violin properly [Clarke also played violin], in drawing the bow straight across the strings in order to produce a pure tone, and in placing the fingers correctly and firmly on the strings. It is astounding how many beginners on musical instruments are allowed to become careless, they themselves not realizing what this negligence in the case of a beginner in music is the same as that of a child who when beginning the study of the multiplication table is permitted to guess at results, such as two times two equals four. I classify all uncorrected errors as "microbes" which, although invisible to the naked eye, are deadly - even more deadly than an animal as big as an elephant. One can run away or hide from or dodge an elephant, but not so with a microbe. These minute organisms multiply rapidly and in large number if not immediately driven out of the system.
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On Mozart:

"The sonatas of Mozart are unique; they are too easy for children, and too difficult for adults. Children are given Mozart to play because of the quantity of notes; grown-ups avoid him because of the quality of notes." - Pianist Artur Schnabel
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On Mastery:
Daniel Bonade in "The Band Director's Guide", by Kenneth L. Neidig, Pub. Prentice Hall, Copyright 1964:

My idea in teaching is to wait until a student is able to master his instrument sufficiently before giving him any solos to play because beginners contract bad habits with solos and sometimes cannot get rid of them. This is just a private opinion, of course.