Paolo Uccello's wife told people that Paolo used to stay up all night in his study trying to work out the vanishing points of his perspective. When she called him to come to bed, he would say "Oh what a lovely thing this perspective is!"
Giorgio VasariThese rough sketches, which are born in an instant in the heat of inspiration, express the idea of their author in a few strokes, while on the other hand too much effort and diligence sometimes saps the vitality and powers of those who never know when to leave off.
Giorgio Vasari