We think of the principles as ways to work with and arrange the elements. This list is an example list. Every author seems to have a slightly different list of Principles. It is about dominance and influence. Most artists put it a bit off center and balance it with some minor themes to maintain our interest.
Some artists avoid emphasis on purpose.
They want all parts of the work to be equally interesting. Harmony - complex but pleasing visual combinations are harmonious. Unity - when nothing distracts from the whole you have unity. Unity without variation can be uninteresting - like driving through western Kansas on the interstate. Unity with diversity generally has more to offer in both art and in life.