The original idea, the sketch, which is so to speak the egg or embryo of the idea, is usually far from being complete; it contains everything, which is simply a mixing together of all parts. Just the thing that makes of this sketch the essential expression of the idea is not the suppression of details, but their complete subordination to the big lines, which are, before all else, to create the impression. The greatest difficulty therefore is that of returning in the picture to that effacing of the details which, however, make up the composition, the web and the woof of the picture.