Applying Sigmund Freud

Sigmund Freud is best known for his theories of the unconscious mind and the defense mechanism of repression. This diagram from http://webspace.ship.edu/cgboer/freud.html depicts Freud's theory quite simply and completely. His theory consists of three main portions, conscious, preconscious, and unconcscious.

The conscious mind is, "what you are aware of at any particular moment, your present perceptions, memories, thoughts, fantasies and feelings.
The preconscious mind is "anything that can easily be made conscious, the memories you are not at the moment thinking about, but can readily bring to mind. Interestingly, these two portions consist of the smaller part of the mind.
The largest portion is the unconcscious, which includes "all the things that are not easily available to awareness, including many things that have their origins there, such as our drives or instincts, and things that are put there because we can't bear to look at them.

The unconcscious portion of our mind is what motivates us, the driving force behind our actions. These include food, sex, art. Sometimes, these portions or our minds are not appealing and dark. As a defense mechanism, we force these underneath and attempt to hide these feelings. This mechanism is often known as the ego defense mechanism.