Perhaps as a student in a high-school art class, you had an experience similar to this--if, in completing an assignment for a painting of a still life or a natural scene, you didn't fill in the background in some manner, the teacher looked at it and said, "It's not finished!"
學生時代上美術課時，也許您會有這種經驗﹘ ﹘不管畫靜物或風景，背景如果不填滿色彩，就被任課老師視為「沒畫完」﹘﹘那有偷懶到不畫背景的道理。