"Excellence is never granted to man but as the reward of labor. It argues no small strength of mind to persevere in habits of industry without the pleasure of perceiving those advances, which, like the hand of a clock, whilst they make hourly approaches to their point, yet proceed so slowly as to escape observation."
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Source : Sir Joshua Reynolds, Edward Malone (1867). “The Works of Sir Joshua Reynolds: Containing His Discourses, Idlers, A Journey to Flanders and Holland, and His Commentary on Du Fresnoy's Art of Painting; to which is Prefixed an Account of the Life and Writings of the Author by Edward Malone”, p.19