Shifting Trends
Trends shift and change in fashion. One such shift in trends is called the Pendulum Swing where fashions move from one extreme to another. For instance, have you even noticed that when gold jewelry is in fashion there is rarely any silver or rose-gold tone jewelry around? That's because the fashion industry is in a pendulum swing where gold jewelry is in abundance while silver is not. This is design to get consumers to buy the latest fashions. The same concept holds true for hemline changes (short miniskirts will eventually be long again with the maxi dress being in fashion over time), neckline changes, and more.
Also consider that only certain focal points on the body will get attention. So if necklines are low (meaning a plunging deep v-neck is in style to reveal more skin at the neckline), then hemlines will shift to be long (causing minimal exposure of skin to the legs). This is intended to only expose certain areas of the body at a time. For example, a sleeveless turtleneck brings emphasis to the arms as having greatest skin-exposure.
There are other fashion theories that also explain other shifting fashion trends. These theories include: Trickle Down, Trickle Up, and Trickle Across which are explained further below.
To represent this concept, the following information is about each theory. The pendulum swing being like a ball at the end of a thread that is swung back and forth to fashion extremes such as the gold to silver jewelry trend, the trickle/flow theories showing a pyramid that represents the various economic classes (top of the pyramid are at the top of the economic pyramid such as royalty and celebrities, middle of the pyramid represents the middle class, and the bottom of the pyramid represents the lower class).