If you are not skillful enough to sketch a man jumping out of a window in the time it takes him to fall from the fourth storey to the ground, you will never be able to produce great works.
As for the ridiculous fear of making things below one's potential abilities... No, there is the root of the evil. There is the hiding place of stupidity I must attack: vain mortal, you are limited by nothing.
Real beauty in the arts is eternal and would be accepted at all periods; but it wears the dress of its century: something of that dress clings to it, and woe to the works which appear in periods when the general taste is corrupted.
In every art we are always obliged to return to the accepted means of expression, the conventional language of the art. What is a black-and-white drawing but a convention to which the beholder has become so accustomed that with his mind's eye he sees a complete equivalent in the translation from nature?
Remember the enemy of all painting is gray: a painting will almost always appear grayer than it is, on account of its oblique position under the light.