The shortest answer would probably be "Perception and Control". Perception being refining the eye to perceive the entire image as a whole as well as perceiving subtlety in shapes/proportions, values, edges, etc. Control being the ability to manipulate the medium _exactly_ how I intend. In the world of music it would be refining your ear and mastering your instrument. Also it was really important for me to keep working through all the barriers and frustrations, just keep going, refine, fix, erase, redraw, until it's just right.