Gestault psychology pg. 68 Stewart

I think that people naturally  use these principles without even thinking about it when they are looking at art. But it may take some knowledge or understanding of this psychology as an artist to deliver an image to a viewer so that the principles get utilized. But an artist may not need to know these principles of Gestault psychology to make a masterpiece. It seems that its helpful information to know to help compose an image "flow" but not a necessity.