During my freshman year at CalArts, our animation teacher Dan Boulos used to come in every week and write a quote on the board to inpire us . He usually got his quotes from "The Art Spirit" by Robert Henri. Here's one on sketching:
People say ,"It is only a sketch." It takes the genius of a real artist to make a good sketch-to express the most important things in life-the fairness of a face-to represent air and light and to do it all with such simple shorthand means. One must have wit to make a sketch. Pictures that have had months of labor expended on them may be more incomplete than a sketch.