"Often you must sacrifice one set of relationships in order to emphasize another more essential one."
This speaks to the limitations of paint when expressing the varied and wide-ranging world of light. If you have nine values in which to express the world, you will need to simplify the complexity of what you see. Otherwise, you will run out of values. If the lightest color you have to express a light source is light yellow, then all other yellows must be subordinated to that one, or the light source won't appear to be light.
There's another aspect to the expression of relationships. Our brains are attracted to variety and contrast. If all relationships are expressed with equal emphasis, the painting that results is one of scattered interest. If essential relationships are expressed clearly and others are subordinated, then the painting shines with expression of the artist's intention.
It is useful, in either case, to know what your painting is about.