"You are not to give up the quick sketch. That work must go on always." Whenever I find myself in need of a mentor, or wanting to hear another artists perspective about the arts (and i don't have an actual ear to bend), I turn to The Art Spirit, a collection of artist/teacher, Robert Henri, notes and lectures. There is advice, criticism, and sound wisdom to be found in this books pages. Since I've been blogging about drawing from life, I thought i might impart a bit of Henri's own words on the subject. "People say, "It's 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 face - to represent air and light and do it all with simple short hand means. One must have wit to make a sketch. Pictures that have months of labor expended on them may be more incomplete than a sketch."
You have to love an artist that will speak so passionately about the quick sketch!