One of the most important things about painting is contrast, not just between light and dark or warm and cool, but between ideas. A thing has its value when placed next to something that has an opposite or contrasting value. The best way to get a true impression of the elements were looking at is by seeing it in contrast with something else. This gives meaning to it. If you are looking at a composition that has only straight lines you can only appreciate it to a certain level. When you are looking at a composition that has straight edges combined with organic edges, the characteristics and purpose of those straight edges become much more powerful, and likewise with the organic edges. This idea can be applied to all abstract properties that construct a painting. Everything between big shapes/small shapes, dark tones/light tones, warm colors/cool colors, saturated colors/greys, areas of detail and information/areas that are quiet or subtle, thin paint/thick paint, textured areas/smooth areas and on and on. I believe this gives vitality and interest to an artwork.