Much like the steelyard principle, balance by isolation identifies the primary subject in a work of art by clearly separating it from other elements in a composition. For example, in the image below, "Racehorses in a Landscape" by Edgar Degas, notice how the one horseman to the far right of the frame is completely isolated from the larger group to the left.
This isolation effect is not only a result of the main subject being separated from the larger group but also because most of the riders in the larger group are moving forward, while the horseman to the right is facing away (as if he was leaving the scene), thereby enhancing the feeling of isolation. This distinct separation is an indicator that the one particular horseman is an important focal point in the design.
In the photograph below, notice how Henri Cartier-Bresson has created a sense of isolation and loneliness by separating the main subject (the woman) from the larger group of figures. This sense of isolation was achieved utilizing selective focus (softening the background) and careful framing (considering the physical space between the woman and the group of figures located in the background as well as the left and right-hand side of the frame).