When an artist wants to place emphasis on some object or element in a work of art that artist will combine different elements and principles to reinforce that intent. For instance, in this painting by Carravgio the emphasis initially appears to be on David, but David is not the focal point. Notice that line of sight from David leads to Goliath's head. That is reinforced by the line of the garment, the foreshortening of David's arm and even the use of chiaroscuro on Goliath's head. In this painting by Sandro Botticelli the focal point is the central figure (presumably Venus). This is reinforced by her central position, the figure of cupid above her, the red garment, and the arch that frames her.
Any element used in a proper way can reinforce any other element. In the texture lecture the discussion of reinforcement focused on the impact of texture on a shape. Usually when a texture reinforces a shape it helps to make that object look more realistic, as in this work by James Tissot. Every object has an implied texture that reinforces the realness (what is expected) of that shape.